US3536062A - Monitoring system for heart rate,respiration rate and blood pressure - Google Patents

Description

United States Patent [72] Inventor Anton .I. Horn 3,058,458 10/1962 Daneman 128/2.06 St. Louis Count Missouri 3.068513 4/1963 Newland et a1. 128/205 3' 2 Appl No 627,262 3,101,082 8/1963 Steen et a1. 128/205 [22] Filed March 30, 1967 3.138.151 6/1964 Chapman et al. 128/205 [451 Patented ct.27, 1970 3236.230 2/1966 Follctt... 128/205 [73] Assignee By mesne assignments 3,347,223 /1967 Pacela 128/21 g f g j Primary E.raminerWilliam E. Kamm 2 Attorneys-Samuel L. Welt, Jon S. Saxe, Bernard S. Leon and a corporation 0 ew Jersey. Jacob Frank [54] MONITORING SYSTEM FOR HEART RATE, ABSTRACT: A solid-state control system simultaneously and RESPIRATION RATE AND BLOOD PRESSURE substantially continuously monitors the blood pressure, heart 28 Claims 5 Drawing Figs rate and respiration rate of a person providing variable length pulses to an clectromagnetically operated, variable-length [52] U.S.Cl 128/2.05, slmkc air pump to comm] the pressurization and dePrcs- 128/11 surization of an artery-occluding inflatable cuff, using a signal [51] InLCl A6115/02 f a heart rate Circuit to a blood pressure circuit, 1 Field ofsearch 128/105- using AC coupling of a respiration rate circuit to the body of 206121 1 8 330/19 the person to avoid grounding of that person's body and to avoid impedance matching adjustments. and using just one [56] References Cited pair of electrodes maintained in good electrical contact with UNlTED STATES PATENTS that person's body by an electrolyte. for both the heart rate 2710.001 6/1955 Frcyburger 128/2115 circuit and the respiration rate circuit to enable a high 2,826,191 3/1958 Burns 128/105 frequency signal from that respiration rate circuit to 2,827.040 3/1958 Gilford 128/205 depolarize that electrolyte.

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r sua-cmcwr w a, 121 J l J I TIMKR L J x9 MIIFR Patented Oct. 27, 1970 Sheet 2 014 Patented 0ct. 27, 197 0- Sheet Patented Oct. 27, 1970 Sheet MONITORING SYSTEM FOR HEART RATE. RESPIRATION RATE AND BLOOD PRESSURE This invention relates to improvements in control systems. More particularly, this invention relates to improvements in control systems that monitor the blood pressure. heart rate, and respiration rate of a person.

It is an object of the present invention to provide an improved control system that can simultaneously and substantially continuously monitor the blood pressure, heart rate, and

respiration rate of a person.

it would be desirable to provide a control system that could simultaneously and substantially continuously monitor the heart rate, the respiration rate, and the blood pressure of a person, and that could display that persons heart rate, respiration rate, and blood pressure in readily readable form. Further, it would be desirable for that control system to actuate an alarm circuit in the event that the person's heart rate. respiration rate and blood pressure failed to remain within closely set upper and lower limits. The present invention provides such a control system; and it is, therefore, an object of the present invention to provide a control system which can simultaneously and substantially continuously monitor the heart rate, respiration rate and blood pressure of a person, that can display that heart rate, respiration rate. and blood pressure in readily readable form, and that can actuate an alarm circuit in the event that heart rate, respiration rate, and blood pressure fail to remain within closely set upper and lower limits.

The control system provided by the present invention has an inflatable cuff that will be disposed adjacent some portion ofa person's body wherein an artery can be occluded sufficiently to cause Korotkoff sounds to be developed. That inflatable cuff must be alternately pressurized and depressurized to cause it to occlude and then free that artery; and the control system provided by the present invention uses an electromagnetically operated. variable-length stroke, air pump to pressurize and depressurize that inflatable cuff. In doing so, that control system eliminates all need of valves and thus obviates the initial cost as well as the cost of maintaining air-controlling valves. Further, that control system can provide closer and more precise control of the pressure supplied to the inflatable cuff. it is, therefore, an object of the present invention to provide a control system wherein an elcetromagnetically operated, variable-length stroke, air pump prcssurizes and then depressurizes an inflatable cuff.

The control system provided by the present invention has a microphone which will be secured to the portion of the persons body wherein the artery will be occluded to cause Korotkoff sounds to be developed; and that microphone will sense those Korotkoffsounds. That microphone also will sense other sounds and it would be desirable to keep as many as practicable of those other sounds from affecting the operation of the air pump. The control system provided by the present invention keeps as many as practicable of those other sounds from affecting the operation of the air pump; and it does so by applying all signals from the microphone to a cascaded bandpass filter and amplifier thus effecting sharp attenuation of all signals below 40 c.p.s. and above 120 c.p.s. and also by isolating the control circuit for the air pump from the output of that cascaded band-pass filter and amplifier except for the short periods of time when the Korotkoff sounds are to be sensed. That control system attains that desirable result by interposing a gate between that cascaded band-pass filter and amplifier and the control circuit for the air pump by using the heart rate circuit to develop a signal each time the person's heart beats, by using that signal to initiate a time delay corresponding to the length of time needed for the surge of blood resulting from that heart beat to reach the occluded portion of the artery, and then opening that gate to permit the signals corresponding to the Korotkoff sounds to actuate the control circuit for the air pump. That gate will be open for just a small portion of the time between consecutive heart beats, and hence most of the sounds sensed by the microphone will be wholly isolated from the control circuit for the air pump; and all of the sounds which are sensed by that microphone while that gate is open will be closely filtered by the cascaded bandpass filter and amplifier. The overall result is that the control system provided by the present invention keeps as many as practicable sounds, other than Korotkoff sounds, from affecting the control circuit for the air pump.

The heart rate circuit and the respiration rate circuit of the control system provided by the present invention avoid all need of grounding the person's body; and this is important because it enables that control system to be used with other devices, systems and equipment without subjecting that person to the risk of electrical shocks due to ground loops through his body and those other devices, systems and equipment. Also, by avoiding all need of grounding the person's body, that control system avoids any aberrations in the readings of the meters of that control system in the event that person touches nearby grounded objects, devices, systems and equipment. Moreover, by avoiding all need of grounding the person's body, that control system reduces the number of electrodes that must be affixed to that persons body. It is, therefore, an object of the present invention to provide a con trol system that obviates all need of grounding the person's body.

The control system provided by the present invention obviates all need of impedance-matching adjustments, even though the impedances of different persons can vary considerably, and even though the impedance of any given person can change materially as that person shifts from a sitting position to a lying position, or vice versa. This is important; because impedance-matching adjustments are time consuming. and they can lead to erroneous adjustments and erroneous readings on the meters. That control system obviates all need of impcdancc-matching adjustments; and it does so by providing AC coupling betweenthc respiration rate circuit thereof and the electrodes attached to the body of the person, and by using a differential input amplifier as the input of the heart rate circuit. It is, therefore, an object of the present invention to provide a control system wherein the respiration rate circuit is AC coupled to the electrodes attached to the body of the person. and wherein a differential input amplifier is used as the input of the heart rate circuit.

An electrolyte is customarily used to provide good electrical contact between the body of a person and the electrodes affixed to that persons body. Where the electrodes are to be affixed to that persons body for appreciable periods of time, the electrolyte tends to polarize; and that polarization would be objectionable. The control system provided by the present invention prevents polarization of the electrolyte used to provide good electrical contact between the body of a person and the electrodes affixed to that person's body, irrespective of how long those electrodes are affixed to that person's body; and it does so by using just one pair of electrodes for both the heart rate circuit and the respiration rate circuit of that control system, and by continually passing a high frequency signal through that electrolyte. That high frequency signal will completely and fully prevent polarization of the electrolyte, and will thus avoid the objectionable results which such polarization can produce.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

in the drawing and accompanying description a preferredembodiment of control system that is made in accordance with the principles and teachings of the present invention is shown and described, but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, FIG. I is a block diagram of one preferred embodiment of control system that is made in accordance with the principles and teachings of the present invention,

FIG. 2A is a schematic diagram of part of the embodiment of control system shown by HQ. 1,

FIG. 2B is' a schematic diagram of another part of the embodiment of control system shown by FIG. 1,

FIG. 2C is a schematic diagram of yet another part of the embodiment of control system shown by FIG. I, and

HG. 3 is a graph showing two frequency response curves.

COMPONENTS OF CONTROL SYSTEM Referring to the drawing in detail, the numeral 20 in FIG. 1 denotes a power supply which has the input terminals thereof connectable to a source of alternating current by conductors 21. In the said one preferred embodiment of control system provided by the present invention, that source of alternating current will apply about 1 l7 volts of 60 c.p.s. alternating current to the input terminals of that power supply; and the positive output terminal of that power supply will apply a regulated positive 12 volts DC to a movable contact 24, the negative output terminal of that power supply will apply a regulated negative 12 volts DC to a movable contact 25, and the AC output terminal of that power supply will apply 100 volts AC to a movable contact 26. Those movable contacts are preferably ganged together to constitute a triple-pole, singlethrow switch 35. A storage battery 22 has the positive terminal thereof connected to the positive output terminal of the power supply 20 and to the movable contact 24; and has the negative terminal thereof connected to the negative output terminal of that power supply and to the movable contact 25. That battery constitutes a stand by source of power; and it will receive battery-charging energy from the power supply 20 rather than supply energy to the movable contacts 24 and 25 as long as that power supply receives power from the conductors 21. However, in the event a power failure cuts off the power that is normally supplied to the conductors 21, or in the event the DC portion of the power supply is injured and becomes unable to supply power to the movable contacts 24 and 25. the battery 22 will automatically and immediately supply power to those movable contacts for several hours.

A conductor 27 connects the movable contact 24 to terminal 51 in FIG. 2A and to terminal 161 in FlG. 2B; and thus can apply a regulated positive 12 volts DC to those terminals, A conductor 28 connects the movable contact 25 to terminal 61 in H6. 2A and to terminal 261 in FIG. 2B; and thus can apply a regulated negative 12 volts DC to those terminals. A conductor 29 connects the movable contact 26 to a terminal 342 in FIG. 2B, and also connects that movable contact to one terminal of an electromagnetically operated, variable-length stroke. flexible diaphragm air pump 540 in FIG. 1; and that conductor will apply l volts AC to that terminal and to that pump.

A free-running multivibrator 23 in FIG. I has the input thereof connected to the conductor 27; and a power stage 47 has one input thereof connected to that conductor, and has the other input thereof connected to the output of the multivibrator 23. That power stage can constitute one or more transistors connected as an electronic switch to selectively connect the conductor 27 to a conductor 31. The multivibrator 23 and the power stage 47 will alternately apply power to, and halt the application of power to, the conductor 31. in the said one preferred embodiment of control system, that multivibrator and power stage alternately apply positive 12 volts DC to the conductor 31 for 100 milliseconds and then halt the application of that voltage to that conductor for 900 milliseconds. That embodiment of control system has a heart rate meter 33, a respiration rate meter 37, and a blood pressure meter 546; and those meters are sensitive. contact less meter relays. Each of those meters has a photocell and a lamp therein which can complete an alarm circuit whenever the needle of that meter reaches an upper adjustable limit, and also has a second photocell and a second lamp therein which can complete a second alarm circuit whenever that needle reaches a lower adjustable limit. The alarm circuits of the heart rate meter 33 have lamps 39 and 41 therein, the alarm circuits of the respiration rate meter 37 have lamps 43 and 45 therein, and the alarm circuits of the blood pressure meter 546 have lamps 548 and 550 therein. In addition, the said one preferred embodiment of control system has a read" lamp 454. While each of those lamps will consume only a small amount of power, the six limit-setting lamps within those meters could, by themselves, drain power from the battery 22 at an undesirably high rate during any periods wherein the power supply 20 was not supplying power to those lamps if that battery had to supply power to those lamps on an uninterrupted basis. if any alarm lamps were to draw power from the battery 22 during those periods on an uninterrupted basis. the drain on that battery would be even higher. By using the multivibrator 23 and the power stage 47 to supply power to the conductor 3'1 for just one tenth of the time, the said one embodiment of control system materially reduces the drain which the lamps of that control system can impose upon the battery 22.

The numerals 30 and 32 denote terminals that will be connected to electrodes which are attachable to the body of a person; and those electrodes will preferably be the standard and usual electrodes that are used with electrocardiographs. A resistor 34 connects the terminal 30 to the anode of a diode 36 and to the cathode of a diode 46. The cathode of the diode 36 and the anode of the diode 46 are connected together and to ground; and they also are connected to the cathode of a diode 44 and to the anode of a diode 38. The anode of the diode 44 and the cathode of the diode 38 are connected together, and they are connected to the terminal 32 by an adjustable resistor 40 and a resistor 42. A capacitor 48 is connected between the right-hand terminal of resistor 34 and the upper terminal of adjustable resistor 40.

The numeral 50 denotes a conductor which has one end thereof connected to the terminal 5!; and a resistor 57, a conductor 59, and a Zener diode 52 connect the other end of that conductor to ground. That Zener diode will coact with that resistor to establish a regulated positive voltage of less than l2 volts at the conductor 59. The numeral 53 denotes a conduc tor which has one end thereof connected to the terminal 61; and a resistor 55 and a Zener diode 56 connect the other end of that conductor to ground. That resistor and that Zener diode will coact to establish a regulated negative voltage of less than 12 volts at a conductor 54 which is connected to the anode of that Zener diode. The Zener diodes 52 and 56, the conductors 54 and 59, the resistors 55 and 57, parts of the conductors 50 and 53, NPN transistors 60, 62, 64, 66, 68, 70 and 72, and the potentiometers, resistors and capacitors associated with those transistors constitute a low-frequency, differential input amplifier. That low-frequency, differential input amplifier is enclosed within a block which is denoted by the numeral 58. An adjustable resistor 63, which is connected in series with a capacitor 65 between the collector of transistor 64 and the base of transistor 66, constitutes the gain adjustment of that amplifier. An adjustable resistor 67, which is connected between the base of transistor 70 and the con ductbr 53, constitutes the zero adjustment" for the signal at the emitter of transistor 72.

The transistor 72 is connected as an emitter follower; and a resistor 76 extends between the emitter of that transistor and a terminal 74. The emitter of that transistor is directly connected to the base of an NPN transistor 78; and it is connected to ground by a diode 82, a junction 77, and a resistor 85. A junction 83, a capacitor 84, and a junction 73 will couple any changes in voltage at the junction 77 to the base of an NPN transistor 86. The collector of the transistor 78 is coupled to the base of the transistor 86 by a capacitor 79. a diode 80, the junction 83, the capacitor 84, and the junction 73. A resistor 81 is connected between the anode of the diode and ground. A resistor 87 connects the collector of transistor 78 to the conductor 50, and thus to positive l2 volts; and a resistor 91 connects the emitter of that transistor to ground. A resistor 89 connects that emitter to the conductor 53, and thus to negative 12 volts. The transistor 78, resistors 8t, 85, 87, 89 and 91, capacitor 79, and diodes 80 and 82 constitute a subcircuit which can respond to positive-going and negativegoing waveforms to produce only positive-going waveforms.

That subcircuit is enclosed within a block which is denoted by the numeral 97.

A resistor 71, the junction 73, and a resistor 75 constitute a voltage divider connected between the conductor 50 and ground; and that voltage divider establishes a positive DC voltage at the base of transistor 86. The collector of that transistor is connected directly to the conductor 50, and thus to positive 12 volts; while the emitter of that transistor is connected to ground by a resistor 69. The transistor 86 is connected as an emitter follower to minimize any loading" of the diodes 80 and 82 of the subcircuit within the block 97. A capacitor 88 couples the emitter of transistor 86 to the base of an NPN transistor 90 which is connected as a stage of amplification. A diode 92 is connected between the collector of transistor 90 and ground; and that diode will bypass to ground substantially all positive-going components of the signals amplified by the transistor 90. A capacitor 93 couples the negative-going signals at the collector of that transistor to the base of an NPN transistor 94 which is connected as a stage of amplification. The collector of the transistor 94 is directly connected to the base of an NPN transistor 95 which is connected as an emitter follower.

A capacitor 96, a resistor 98, and a conductor 101 couple the emitter of transistor 95 to the input of a phase-shift oscillator 99 in FIG. 2C; and the components of that oscillator are dimensioned so it will act as a filter. Specifically, the components of that oscillator are dimensioned so it will respond to signals having leading edges with slopes comparable to those of a 25 c.p.s. sinusoid to become shock excited, but will not become shock excited in response to signals having leading edges with materially different slopes. A capacitor 111 and a resistor 113 couple the output of oscillator 99 to the input ofa phase-shift oscillator 115; and the components of the latter oscillator also are dimensioned so it will act as a filter. Specifically, the components of oscillator 115 are dimensioned so it will respond to signals having leading edges with slopes comparable to those of a 25 e.p.s. sinusoid to become shock excited, but will not become shock excited in response to signals having leading edges with materially different slopes. The two oscillators 99 and 115 coact to provide much sharper rejection of signals with undesired slopes for the leading edges thereof than either of those oscillators could provide. A capacitor 117 couples the output of the oscillator 115 to the base of an NPN transistor 119 which is connected as a stage of amplification; and the collector of that transistor is directly connected to the base of an NPN transistor 121 which is connected as an emitter follower.

Resistors 125 and 127 constitute a voltage divider which is connected between the conductor 50 and ground; and that voltage divider establishes a predetermined positive voltage at the cathode of a diode 123. The anode of that diode is connected to the emitter of transistor 121; and that diode will be back-biased until a signal appears at the emitter of that transistor which is more positive than the predetermined voltage at the cathode of that diode. As a result, the diode 123 and the resistors 125 and 127 constitute a level detector 120. A capacitor 129 couples the output of that level detector to the base of an NPN transistor 131 which is connected as a stage of amplification. A resistor 133 and a diode 135 are connected in series between the collector of transistor 131 and ground; and that diode will tend to bypass to ground any positive-going components in the signals at that collector. A capacitor 141 is connected between the resistor 133 and the input terminal of a monostable multivibrator 145; and a resistor 143 is connected between that capacitor and ground.

The monostable multivibrator 145 will respond to a negative-going pulse at the input terminal thereof to develop a positive-going, rectangular pulse at the output thereof. in the said one embodiment of control system, that pulse will have a duration of 100 milliseconds. A capacitor 147 and a diode 149 are connected in series between the output of the multivibratior 145 and a terminal 100; and a resistor 151 connects the anode of that diode to a conductor 107 which is connected to conductor 53 and thus to negative 12 volts. As a result, that diode will be back-biased until the multivibrator 145 develops a positive-going pulse, and the capacitor 147 couples that pulse to the anode of that diode.

The output of the monostable multivibrator 145 is connected to a rate circuit by a conductor 137, and it is coupled to the base of an NPN transistor 136 by conductor 137 and series-connected capacitor 132 and resistor 138. The rate circuit 105 consists of a series-connected resistor 104 and capacitor 102; and that capacitor has one terminal thereof connected to ground. A junction 103 between that resistor and that capacitor is connected directly to the base of an N PN transistor 110, and is connected to the collector of an NPN transistor 134 by series-connected diodes 148 and 150. A resistor 142, the collector-emitter circuit of transistor 136, and a resistor 146 are connected in series between the conductors 50 and 53. A capacitor 144 is connected in parallel with the series-connected resistor 146 and collector-emitter circuit of transistor 136. A resistor is connected between the base of transistor 136 and the conductor 53.

A conductor 139 connects a resistor 124 and a potentiometer 126 between the conductor 59 and ground; and that resistor and potentiometer constitute a voltage divider. A resistor 128 and an adjustable resistor 130 connect the movable contact of the potentiometer 126 to the base of an NPN transistor 108. That transistor, the NPN transistor 110, a PNP transistor 112, an NPN transistor 114, the resistors 124 and 128, the potentiometer 126, the adjustable resistor 130,.the capacitor and the other resistors associated with those transistors constitute an operational amplifier; and that operational amplifier is enclosed within a block denoted by the numeral 106. The transistor 114 of that operational amplifier is connected as an emitter follower; and a resistor 116 is connected between the emitter of that transistor and a terminal 118.

A conductor in H6. 28 has one end thereof connected to the terminal 161, and thus to positive 12 volts, and it has the other end thereof connected to ground by a resistor 169, a junction 171 and a Zener diode 167. That resistor and Zener diode will develop a regulated DC positive voltage of less than 12 volts at the junction 171. A conductor 164 is connected to the junction 171, and a conductor 166 is connected to ground; and a potentiometer 168 is connected between those conductors, and thus between a regulated DC positive voltage and ground. The movable contact of that potentiometer and a resistor 170 apply a regulated DC positive voltage to the gate of a field effect transistor 162; and the drain of that transistor is connected directly to the conductor 164 while the source of that transistor is connected to the grounded conductor 166 by a resistor 172. A microphone 158 has one terminal thereof connected to ground, and has the other terminal thereof coupled to the gate of the field effect transistor 162 by a capacitor 160. That microphone must be capable of being held closely adjacent some portion of the body of a person wherein an artery can be occluded sufficiently to cause Korotkoff sounds to be developed and to be sensed by that microphone. 1n the said one preferred embodiment of control system. the microphone 158 is small enough to be taped to a finger of a person; and that microphone will usually be taped to that finger distally of an inflatable cuff 538 in FIG. 1 which will be suitably secured to that. finger.

An NPN transistor 174 has the collector thereof connected to conductor 164 by a resistor 176, and has the emitter thereof connected to grounded conductor 166 by a resistor 178 and parallel-connected resistor 180 and capacitor 182. The base of that transistor is connected to the right-hand terminal of resistor 172. An NPN transistor 192 has the collector thereof connected to conductor 164 by a resistor 194, and has the emitter thereof connected to grounded conductor 166 by a resistor 196 and parallel-connected resistor 198 and capacitor 200. Resistors 186 and 188 constitute a voltage divider connected between the conductors 164 and 166, and the junction between those resistors is connected to the base of transistor 192. A capacitor 190 is connected between that junction and the grounded conductor 166; and a capacitor 184 couples the collector of transistor 174 to the base of transistor 192. An NPN transistor 210 has the collector thereof connected to conductor 164 by a resistor 212, and has the emitter thereof connected to grounded conductor 166 by a resistor 214 and parallel-connected resistor 216 and capacitor 218. Resistors 204 and 206 constitute a voltage divider connected between the conductors 164 and 166; and the junction between those resistors is connected to the base of transistor 210. A capacitor 208 is connected between that junction and the grounded conductor 166; and a capacitor 202 couples the collector of transistor 192 to the base of transistor 210. An NPN transistor 228 has the collector thereof connected to conductor 164 by a resistor 230, and has the emitter thereof connected to grounded conductor 166 by a resistor 232 and parallel-connected resistor 234 and capacitor 236. Resistors 222 and 224 constitute a,voltage divider connected between the conductors 164 and 166, and the junction between those resistors is connected to the base of transistor 228. A capacitor 226 is connected between that junction and the grounded conductor 166; and a capacitor 220 couples the collector of transistor 210 to the base of transistor 228. An NPN transistor 246 has the collector thereof connected to conductor 164 by a resistor 248, and has the emitter thereof connected to grounded conductor 166 by a resistor 250 and parallel-connected resistor 252 and capacitor 254. Resistors 240 and 242 constitute a voltage divider connected between the conductors 164 and 166, and the junction between those resistors is connected to the base of transistor 246. A capacitor 244 is connected between that junction and grounded conductor 166; and a capacitor 238 couples the collector of transistor 228 to the base of transistor 246. An NPN transistor 256 has the collector thereof connected directly to conductor 164, and has the emitter thereof connected to ground by a resistor 258. The base of that transistor is connected directly to the collector of transistor 246.

The transistor 174 and its associated capacitor and resistors constitute a band-pass filter and amplifier; and. similarly. each of transistors 192,210, 228 and 246 and its associated capacitors and resistors constitutes a band-pass filter and amplifier. The various band-pass filters and amplifiers, of which the transistors 174, 192. 210, 228 and 246 are component parts. are interconnected as a cascaded band-pass filter and amplifier 259; and that cascaded band-pass filter and amplifier has a frequency response curve which is important and extremely desirable. That frequency response curve is generally denoted by the numeral 269 in FIG. 3; and it is markedly different from the dashed-line frequency response curve 271 which was obtained from just a single band-pass filter and amplifier. Not only is the curve 269 free from any "humpsfisuch as the hump 273 in the curve 271, but it has a fast roll-off below 40 c.p.s. whereas the curve 271 does not. Specifically, the frequency response curve 269 has a slope of 24 decibels per octave below 40 c.p.s. whereas the frequency response curve 271 has a slope of only 6 decibels per octave below 40 c.p.s. As a result, the cascaded band-pass filter and amplifier 259 can strongly reject low frequency signals, such as signals corresponding to a person's pulse, which the microphone 158 will sense; whereas a single band-pass filter and amplifier could not appreciably attenuate such signals. it should also be noted that the frequency response curve 269 has a rapid roll-off above 120 c.p.s. whereas the frequency response curve 271 does not. Consequently, the cascaded band-pass filter and amplifier 259 can strongly reject signals above as well as below its passband of 40 l c.p.s. and can thus pass signals which truly correspond to the Korotkoff sounds and which are essentially free from other signals and noise.

The resistors 176, 194, 212, 230 and 248 coact with the resistors 178, 196, 214, 232 and 250 to determine the gain for the band-pass filters and amplifiers that are interconnected to constitute the cascaded band-pass filter and amplifier 259. The resistors 180, 198, 216, 234 and 252 determine the bias points of the transistors of those band-pass filters and amplifiers.

A conductor 233 has one end thereof connected to the terminal 261, and thus to negative 12 volts; and a conductor 374 has one end thereof connected to that conductor. The numeral 221 denotes an NPN transistor which has the emitter thereof connected to the conductor 233 by a resistor 219, and has the collector thereof connected to the conductor 165 by a resistor 223. Resistors 227, 215 and 231 constitute a voltage divider connected between conductors l65 and 233; and the junction between the resistors 215 and 231 isiconnected to the base of transistor 221. The numeral 22 5denotes an NPN transistor which has the collector thereof connected to the conductor 165 by the resistor 227, and has the emitter thereof connected to the conductor 233 by a diode 229 and the resistor 219. The base of the transistor 225 is connected to conductor 165 by a resistor 235; and the collector of transistor 221 is coupled to that base by a capacitor 237. The transistors 221 and 225, capacitor 237, resistors 215,219,223, 227, 231 and 235, and the diode 229 constitute a monostable multivibrator 217. In the said one preferred embodiment of control system provided by the present invention, that monostable multivibrator will respond to the application of a positivegoing pulse to the base of transistor 221 to establish a positivegoing pulse at the collector of transistor 225 and to maintain that positive-going pulse for l30milliscconds. A terminal 263 is connected to the terminal and a conductor 265 and a capacitor 260 couple that terminal to the base of transistor 221. As a result, the development of a positive-going pulse at the terminal 100 will cause a positive-going pulse to be established at the collector of transistor 225.

The numeral 241 denotes an NPN transistor which has the emitter thereof connected to conductor 233 by a resistor 243, and which has the collector thereof connected to conductor by a resistor 245. An NPN transistor 247 has the emitter thereof connected to conductor 233 by a diode 249 and the resistor 243, and has the collector thereof connected to conductor 165 by an adjustable resistor 264, a resistor 266, a junction 268, and a diode 270. The base of that transistor is connected to the conductor 165 by a resistor 257'. and the collector of transistor 241 is coupled to that base by a capacitor 255. Resistors 253 and 251 connect the collector of transistor 247 to conductor 233; and the junction between those resistors is connected to the base of transistor 241. The transistors 241 and 247, capacitor 255, diode 249, and resistors 243, 245. 251. 253 and 257 constitute a monostable multivibrator 239. in the said one preferred embodiment of control system, that monostable multivibrator will respond to the application of a negative-going pulse to the base of transistor 247 to establish a positive-going pulse at the cathode of diode 270 and to maintain that positive-going pulse for l70 milliseconds.

The transistor 256 of the cascaded band-pass filter and amplifier 259 is connected as an emitter follower; and a conductor 274 and a capacitor 272 couple the emitter of that transistor to the junction 268. The adjustable resistor 264, the resistor 266, the junction 268, and a resistor 276 constitute a voltage divider connected between conductor 165 and conductor 233', and the diode 270, the collector-emitter circuit of NPN transistor 247, the diode 249, and the resistor 243 are connected in series with each other but in parallel with the resistor 276. Also, the series-connected resistors 253 and 251 are connected in parallel with the series-connected collectoremitter circuit of transistor 247, diode 249 and resistor 243. A diode 284 and a resistor 290 are connected between the junction 268 and ground; and the junction between that diode and that resistor is connected to the base of an NPN transistor 278. Resistors 288 and 286 connect the collector of that transistor to the conductor 165, while the emitter of that transistor is connected directly to ground. The diodes 270 and 284, the transistor 278, adjustable resistor 264, and resistors 266, 276, 286, 288 and 290 constitute an And gate; and that And gate is denoted by the numeral 295. That And gate will back-bias the diode 284, and thus keep the transistor 278 nonconductive, until the transistor 247 is rendered nonconductive and the capacitor 272 couples positive-going signals to the anode of that diode to forward-bias that diode.

The junction between the resistors 286 and 288 is connected to the base of a PNP transistor 282; and that transistor has the emitter thereof connected directly to the conductor 165, and has the collector thereof connected to conductor 233 by resistors 292, 294 and 296, the base-emitter circuit of an NPN transistor 298, and a resistor 316. An NPN transistor 280 has the base thereof connected to the collector of transistor 282, has the collector thereof connected to conductor 165 by the resistor 286, and has the emitter thereof connected to conductor 233 by the resistors 294 and 296, the base-emitter circuit of transistor 298, and the resistor 316. A capacitor 300 is connected between conductor 165 and the junction between the resistors 294 and 296. Resistors 302, 308 and 310 constitute a voltage divider connected between the conductors 165 and 233; and the junction between resistors 302 and 308 is connected to the collector of transistor 298, while the junction between resistors 308 and 310 is connected to the base of an NPN transistor 312. The collector of transistor 298 also is connected to a fixed contact 306 of a four-pole double-throw switch 323. That switch has a movable contact 343 and a fixed contact 347 in FIG. 2A, and has movable contacts 322, 325 and 333 and fixed contacts 320, 327 and 341 as well as 306 in FIG. 2B. The movable contacts 322, 325, 333 and 343 are ganged together; and they will be in the positions shown by the drawing whenever a person's diastolic blood pressure is to be sensed, and will be shifted in the clockwise direction whenever that person's systolic blood pressure is to be sensed. The emitter of transistor 298 is connected to the conductor 233 by the resistor 316; and the emitter of transistor 312 also is connected to that conductor by that resistor. The collector of transistor 312 is connected directly to the fixed contact 320 of switch 232, and is connected to the conductor 165 by a resistor 314. The transistors 280, 282, 298 and 312. the capacitor 300, and the resistors 286, 292. 294, 29 6, 302, 308, 310 and 316 constitute a timer 319. in the said one preferred embodiment of control system, that timer provides a delay of l V2 seconds.

The movable contact 322 of switch 323 is connected to the base of a PNP transistor 326 by a junction 324 and a resistor 331, and is connected to the base of an NPN transistor 336 by the junction 324 and a resistor 338. A resistor 328 and a resistor 330 constitute a voltage divider connected between conductor 165 and ground, and the junction between those resistors is connected to the emitter of transistor 326. The collector of that transistor is connected to a terminal 335 by a conductor 334; and a resistor 332 is connected between that collector and the conductor 233. The transistor 326 and the resistors 328, 330 and 331 constitute a meter inhibiter 337.

A unijunction transistor 340 has the base-two thereof connected to the terminal 342 by a resistor 350, a resistor 344 and a diode 345; and a resistor 346 and a Zener diode 348 connect the junction between the resistors 344 and 350 to ground. The base-one of that unijunction transistor is connected to ground by a resistor 352, and also is directly connected to the gate ofa controlled rectifier 442. That controlled rectifier will preferably be a silicon controlled rectifier; and the cathode thereof will be grounded, while the anode thereof will be connected to a terminal 362 by a resistor 440. A capacitor 360 is connected between the terminal 362 and ground; and a resistor 363 and a diode 365 connect the anode'ofthe controlled rectifier 442 to the terminal 342. A capacitor 354 is connected between the emitter of unijunction transistor 340 and ground; and a capacitor 402 and the collector-emitter circuit of the transistor 336 are connected in series with each other and are connected in parallel with the capacitor 354 by junctions 400 and 408. A discharge diode 356 is connected in parallel with the capacitor 354 and with series-connected capacitor 402 and the collector-emitter circuit of transistor 336. The capacitors 354, 360 and 402, the diodes 345, 356

and 365, the Zener diode 348, the controlled rectifier 442, the transistor 336, and the resistors 344, 346, 352, 363 and 440 constitute a pump controller 371.

The numeral 359 denotes a normally open pushbutton; and one fixed contact of that pushbutton is directly connected to the conductor 374 and thus to negative 12 volts while the other fixed contact of that pushbutton is connected to the base of an NPN transistor 366 by resistors 351 and 353. The junction between those resistors is connected to the conductor and thus to positive l2 volts by resistors 355 and 368 and a conductor 364; and a resistor 370 connects the junction between the resistors 355 and 368 to the collector of transistor 366. A resistor 372 connects the emitter of that transistor to i the conductor 374 and thus to negative 12 volts. A capaci tor 357 is connected between the junction of resistors 351, 353 and 355 and the conductor 374. A resistor 380 connects the collector of transistor 366 to the base of an NPN transistor 376;'and a resistor 384 extends between the base of the latter transistor and the conductor 374. The resistor 372 connects the emitter of transistor376 to the conductor 374, and a resistor 378 connects the collector of that transistor to the conductor 364. The transistors 366 and 376, the capacitor 357, and the resistors associated with those transistors constitute a timer 369; and that timer will successively render the transistor 366 conductive at the saturation level while the transistor 376 is cut off, and will then render the transistor 376 conductive at the saturation level while the transistor 366 is cut off. In the said one embodiment of control system, that timer will render the transistor 366 conductive at the saturation level for 4 minutes, and will then render the transistor 376 conductive at the saturation level for l minute.

A resistor 382 and the anode-to-cathode circuit of a controlled rectifier 386 are connected between the collector of transistor 366 and ground; and that controlled rectifier preferably is a silicon-controlled rectifier. A resistor 388 is connected between the gate of that controlled rectifier and ground; and a conductor 392. a resistor 329. and a resistor 390 connect a terminal 394 to that gate. The movable contact 325 and the fixed contact 327 of switch 323 effectively short" the resistor 329 whenever that switch is in the diastolic blood pressure-sensing position shown by the drawing. The terminal 394 is connectable to the blood pressure meter 546. A resistor 396 and a diode 398 connect the junction between resistor 382 and the anode of controlled rectifier 386 to the junction 400. The controlled rectifier 386. the diode 398, the resistors 329, 370, 382, 388, 390 and 396, and the switch contacts 325 and 327- constitute a fast-pressurization subcircuit;

and that subcircuit is denoted by the numeral 399.

A diode 430, a resistor 428, and a resistor 426 coact with the resistor 378 to constitute a voltage divider connected between the conductor 364 and ground; and the junction between resistors 428 and 426 is connected to the base of an NPN transistor 432. A resistor 423 has one terminal thereof connected to the junction between resistors 426 and 428; and the other terminal of that resistor is isolated from ground by the contacts 333 and 341 of switch 323 whenever that switch is in the diastolic blood pressure-sensing position but is connected directly to ground by those contacts whenever that switch is in the systolic blood pressure-sensing position. The emitter of the transistor 432 is grounded, and the collector of that transistor is connected directly to the junction 400. A PNP transistor 424 has the collector thereof connected to the base of transistor 432; and the emitter of that transistor is connected to the junction 400 by resistors 422 and 420, and also is connected to that junction by series-connected resistor 422, adjustable resistor 421, diode 425, and Zener diode 427. That adjustable resistor, diode and Zener diode constitute a compensating network 429. The junction 394 is directly connected to the junction between resistors 420 and 422 and adjustable resistor 421 by the conductor 392 and a conductor 393. A diode 434 is connected between the base of transistor 424 and the collector of transistor 432, and diodes 436 and 438 are connected in series between the base of transistor 424 and the junction 171 by a conductor 439. A resistor 404 and "tor 364 and the junction 400 by the junction 408. The

transistors 424 and 432, the diodes 434, 436 and 438, and resistors 422, 423 and 426 constitute a pressure-limiting subcirftcuit 431.

The junction between the anode of diode 430 and the collector of transistor 376 is connected to the base of a PNP transistor 441 by a conductor 452 and a resistor 450. The emitter of the latter transistor is directly connected to the conductor 165 by a conductor 448, and the collector of that transistor is connected to the conductor 374 by resistors 462 and 460. A resistor 446 is connected between the emitter and base of transistor 441. The base of an NPN transistor 456 is connected to the junction between resistors 462 and 460; and the emitter of that transistor is connected directly to the conductor 374, while the collector of that transistor is connected to a terminal 455. The negative terminal of the blood pressure meter 546 is connected to that terminal by a conductor 547, as shown by FIG. 1. The lamp 454 has one lead thereof connected to the terminal 455 and has the other lead thereof connected to the conductor 31, also as shown by FIG. 1. The

transistors 441 and 456 and the resistors 446, 450, 460 and 462 constitute a driver for the lamp 454 and for the blood pressure meter 546 and the lamps therein; and that driver is I denoted by the numeral 457.

The numeral 464 in FIG. 2A denotes a conductor which has 5 the right-hand end thereof connected to the conductor 50, *and thus to positive 12 volts. A resistor 466, a junction 467,

and a Zener diode 468 connect the left-hand end of that conductor to ground, and thus establish a regulated positive voltbase of an NPN transistor 486. A terminal 484 is connected to the junction between the resistors 478 and 480 of that latter voltage divider; and that terminal will be connected to a pressure transducer 544 which can sense a variable pressure and which can supply a signal to that terminal which varies lineraly with that pressure.

A resistor 488 connects the collector of transistor 486 to the conductor 464, and also connects the base of an NPN transistor 490 to that conductor. A resistor 496 and a conductor 492 connect the emitter of transistor 486 to the conductor 53 and thus to negative 12 volts. The collector of transistor 490 is connected directly to the conductor 464. while the emitter of that transistor is connected to the conductor 492 by a resistor 498. An NPN transistor 494 also has the emitter thereof connected to the conductor 492 by the resistor 498, and it has the collector thereof connected to the conductor 464 by a resistor 500. A resistor 504 connects the conductor 464 to the base of transistor 494 and to the collector of transistor 502. A resistor 506 and a capacitor 508 are connected in series between the junction of the collector of transistor 486 and the base of transistor 490 and the junction of the collector of transistor 502 and the base of transistor 494. The collector of transistor 494 is directly connected to the base of a PNP transistor 510; and a diode 528 connects the conductor 464 to the emitter of the latter transistor, while a resistor 516 connects the collector of that latter transistor to the conductor 53. The collector of transistor 510 is directly connected to the base of an NPN transistor 512; and the collector of the latter transistor is connected to the conductor 464 by a resistor 514, while the emitter of that latter transistor is connected to the conductor 53 by a resistor 518, is coupled to the resistor 520 by a capacitor 530, is connected to the latter resistor by a series-connected adjustable resistor 524 and resistors 523 and 522, and is directly connected to a terminal 395. That terminal, as well as the terminal 394, is connected to the blood pressure meter 546. The contacts 343 and 347 of switch 323 effectively short the resistor 523 whenever that switch is in the diastolic blood pressure-sensing position shown by the drawing. A diode 526 is connected between thefbase of transistor 494 and the collector of transistor 512. The transistors 486, 490, 494, 502, 510 and 512, the capacitors 508 and 530, the diodes 526 and 528, and the resistors associated with those transistors constitute an operational amplifier 529. The adjustable resistor 474 constitutes the zero" adjustment of that operational amplifier.

The outlet of the pump 540 is connected to the inlet of a reservoir 534; and that reservoir is large enough to tend to smooth out the pressure pulsations caused by the successive strokes of that pump. That reservoir has a vent 536 which continuously places the interior of that reservoir in communication with the atmosphere external of that reservoir. The outlet of that reservoir is connected to the inlet of an orifice 542; and that orifice supplies air to the inflatable cuff 538. That orifice will additionally smooth out the pressure pulsations caused by the successive strokes of the pump 540. The pressure transducer 544 is connected to the inflatable cuff 538, and will thus sense the pressure within that cuff.

Numerals 552 and 554 in HO. 1 denote terminals that are connectable, respectively, to the terminals 30 and 32 of FIG, 2A and thus to electrodes that can be affixed to the body of a person. Terminal 552 is coupled to the center tap of the secondary winding 560 of a transformer 562 by a capacitor 556', and terminal 554 is coupled to the lower terminal of that secondary winding by a capacitor 558. The primary winding 564 of that transformer has a capacitor 566 connected in parallel with it to constitute a tuned circuit; and the lower terminals of that capacitor and primary winding are grounded. The upper terminals ofthat capacitor and primary winding are connected to a block 590 by a junction 568 and a conductor 109, and are connected to the collectors of a PNP transistor 574 and of an NPN transistor 576 by junction 568 and aju nction 570. A terminal 578 is connectable to terminal 51, and thus to positive l2 volts; and a resistor 580 connects the former terminal to the emitter of transistor 574, while a resistor 582 connects that former terminal to the base of that transistor. A terminal 584 is connectable to terminal 61, and thus to negative 12 volts; and a resistor 586 connects the former terminal to the emitter of transistor 576, while resistor 588 connects that terminal to the base of that transistor. The numeral 590 denotes a block that is coupled to the base of transistor 574 by a capacitor 592, and that is coupled to the base of transistor 576 by a capacitor 594. A conductor 177 connects the block 590 with a block 572', and the output of the latter block is connected to the input of the respiration rate meter 37.

The terminals 552 and 554, the transformer 562, the capacitors 556, 558, 566, 592 and 594, the transistors 574 and 576, and the resistors 580, 582, 586 and 588 can be identical to the corresponding terminals, transformer, capacitors, transistors, and resistors disclosed in the concurrently filed Control System patent application Ser. No. 627,034 of Anton .l. Horn and Christopher G. Kuni. The block 590 contains a phase-shift oscillator, a detector, an operational amplifier, and other components of said patent application; and the block 572 contains a frequency multiplier, a monostable multivibrator, a rate circuit, an operational amplifier, and other components of said patent application. The blocks 572 and 590 can be identical to the correspondingly numbered blocks in said patent application.

CONNECTIONS OF CONTROL SYSTEM The terminal 552 in FIG. 1 will be connected to the terminal 30 in FIG. 2A, and then those terminals will be connected to an electrode that can be affixed to the body of a person. Similarly, the terminal 554 in H0. 1 will be connected to the terminal 32 in FIG. 2A, and then those terminals will be connected to a second electrode that can be affixed to that persons body. Those electrodes will preferably be disposed at opposite sides of the thoracic cage of that person, and they will be placed in good electrical contact with that persons body by means of an electrolyte. Those electrodes and that electrolyte can be the standard and usual electrodes and electrolyte used in the eleetrocardiograph art.

The terminal 51 of FIG. 2A, the terminal 161 of FIG. 2B, and the terminal 578 of FIG. 1 will be connected to the conductor 27. The terminal 61 of FIG. 2A, the terminal 261 of FIG. 2B, and the terminal 584 of FIG. 1 will be connected to the conductor 28. The terminal 342 of FIG. 23 will be connected to the conductor 29 of FIG. 1, and also will be connected to one terminal of the pump 540. The other terminal of that pump will be connected to the terminal 362 of FIG. 2B.

The terminal 100 in FIG. 2C will be connected to the terminal 263 in FIG. 2B, and the terminal 484 in FIG. 2A will be connected to the pressure transducer 544 in FIG. 1. The terminal 118 in FIG. 2A will be connected to the input of the heart rate meter 33, the terminals 394 and 395 in FIGS. 2B and 2A, respectively. will be connected together and then to the input of the blood pressure meter 546. the terminal 335 in FIG. 28 will be connected to the inhibit" terminal of that blood pressure meter, and the terminal 455 in FIG. 28 will be connected to the negative terminal of that blood pressure meter. The terminal 74 in FIG. 2A can be connected to a recorder, an oscilloscope, or other instrument which utilizes an analog-type electrocardiograph signal. The terminals 21 in FIG. I can then be connected to a source of I 17 volts. 60 cycle. single-phase, alternating current. The inflatable cuff 538 will be affixed to a finger ofa person; and the microphone 158 will be taped to that finger -usually distally of that inflatable cuff.

It will be noted that only two electrodes need be affixed to the person's body both the heart rate circuit and the respiration rate circuit being connected to the same pair of electrodes. The use ofjust two electrodes is desirable, because the skin of a person can develop a physiological reaction to the electrolyte which is used to assure good electrical contact between the electrodes and that person's skin; and the fewer the electrodes, the less electrolyte that is needed and the smaller the overall physiological reaction. Furthermore, the use of just two electrodes simplifies the problem of holding those electrodes in good electrical contact with that persons skin.

It will be noted that the resistor 34 in FIG. 2A, the base-collector circuit of transistor 60, the collector resistor of that transistor, and resistor 57, or the resistor 34, the upper section of the base-biasing potentiometer for the transistor 60, the upper base-biasing resistor for that transistor, and the resistor 57 are interposed between the terminal 30 and the conductor 50. In the said one preferred embodiment of control system, the resistor 34 has a resistance of one million ohms; and it will effectively keep a hurtful positive DC voltage or current from conductor 50 from reaching the body of the person. Even if that resistor should, somehow, become shorted", the resistor 57, the collector resistor, and the collector-base circuit of transistor 160, or the resistor 57, the upper base-biasing resistor, and the upper section of the base-biasing potentiometer for that transistor would keep any hurtful positive DC voltage or current from reaching the body of the person. Similarly, the resistor 42, the adjustable resistor 40, the lower base-biasing resistor for transistor 64, and the resistor 55 are interposed between the terminal 32 and the conductor 53. In the said one preferred embodiment of control system, the resistance of the resistor 42 is one million ohms; and that resistor will keep any hurtful negative DC voltage or current from reaching the body of the person. Even if the resistor 42 should, somehow, become shorted, the adjustable resistor 40, the lower basebiasing resistor of transistor 64, and the resistor 55 would keep any hurtful negative DC voltage or current from reaching the body of the person.

It should also be noted that the diode 36 is connected between the movable contact of the base-biasing potentiometer for transistor 60 and ground, and that the diode 44 is connected between the lower base-biasing resistor of transistor 64 and ground. Each of those diodes will limit the maximum voltage which ean be developed across it to less than about onehalf of a volt; and hence it will limit the voltage which can be applied to the resistor connected between its anode and the persons body to less than one-half of a volt. Further, in the event that resistor should, somehow, become shorted", that diode would limit the voltage which that "shorted resistor could apply to the body of a person to a level below about onehalf of a volt. The overall result is that the body of the person will be fully protected against any and all potentially hurtful positive DC voltage or current and against any and all potentially hurtful negative DC voltage or current from the heart rate circuit.

The transformer 562 and the capacitors 556 and 558 of the respiration rate circuit will effectively isolate the body of the person from any and all positive and negative DC voltages or currents in the respiration rate circuit. Consequently, that transformer and those capacitors will protect that person against any and all potentially hurtful positive or negative DC voltages or current from that circuit. Even if the transformer 562 were, somehow, to become *shorted. the capacitors 556 and 558 would continue to isolate the person from all positive and negative DC voltages or currents in the respiration rate circuit. Similarly, if either or both of the capacitors 556 and 558 were. somehow, to bccome shorted", the transformer 562 would continue to isolate the body of the person from all positive and negative DC voltages or currents in the respiration rate circuit.

The electrodes that will be connected to the terminals 30 and 552 and to the terminals 32 and 554 will constitute the only direct electrical contact between the body of a person and the control system provided by the present invention. A plurality of electrical impedances will be interposed between each of those electrodes and the positive and negative DC voltages or currents in that control system; and those impedances will be of such a nature and will be so dimensioned that they will keep any potentially hurtful positive or negative DC voltages or currents in that control system from reaching that person's body. Moreover, those impedances will be of such a nature and will be so dimensioned that they will keep any potentially hurtful positive or negative DC voltages or currents in that control system from reaching that person's body even if one of those impedances should, somehow, become shorted. Consequently, the control system provided by the present invention is made doubly safe to use.

The heart rate circuit of the control system provided by the present invention does not require the body of the person to be grounded, and neither does the respiration rate circuit of that control system require that persons body to be grounded. This is important; because it will protect that person against hurtful shocks, due to ground loops extending through his body, which could develop if that heart rate circuit or that respiration circuit required that persons body to be grounded, and if that control system was connected to another device, system or equipment which was grounded. Furthermore, because neither the heart rate circuit nor the respiration rate circuit of that control system requires the body of the person to be grounded, the readings of the meters of that control system will not be aberrated or distorted in the event that person accidentally touches a nearby object, device, system or equipment which is gounded.

OPERATION OF PUMP CONTROLLER which is shown by FIGS. 2A and 2B. Thereafter, the switch 35 will be closed to enable the power supply to apply a positive voltage to the conductor 27, to apply a negative voltage to the conductor 28, and to apply 100 volts AC to the conductor 29.

During the first positive-going half-cycle of the AC applied to the conductor 29 --and thus to the terminal 342 current will flow from that terminal via diode 345, resistors 344 and 346, and Zener diode 348 to ground; and, almost immediately, the voltage at the junction between those resistors and hence at the base-two of unijunction transistor 340 -will reach a predetermined value. Direct current will be flowing from terminal 161 to capacitor 354 via conductors 165 and 364, and then either through series-connected resistors 368, 370, 382 and 396, diode 398, and junctions 400 and 408, or through resistor 404, adjustable resistor 406, and junction 408. The overall ohmic resistance of the parallel-connected resistive paths is substantially less than the overall ohmic resistance of either of those paths, and hence the capacitor 354 will charge quite rapidly. The capacitor 402 and the collectoremitter circuit of transistor 336 are connected in series with each other and in parallel with the capacitor 354; but the transistor 336 will be nonconductive, and hence substantially no current will flow through the capacitor 402. As current started flowing through capacitor 354, current also started flowing from terminal 161 via conductors 165 and 364, resistors 368, 370, 380 and 384, and conductors 374 and 233 to terminal 261; and the resulting positive voltage at the base of transistor 376 will render that transistor conductive. The resulting negative voltage at the collector of that transistor will back-bias the diode 430, and thus render the pressure-limiting subcircuit 431 inactive.

The capacitor 354 will become sufficiently charged. in less than one half-cycle of the AC applied to the terminal 342, to cause the voltage across that capacitor to reach the emitter peak point voltage of the unijunction transistor 340 and thereby render that unijunction transistor conductive. That capacitor will then discharge through the emitter-base-one circuit of that unijunction transistor and resistor 352; and the resulting voltage drop across that resistor will cause sufficient current to flow through the gate-to-cathode circuit of the controlled rectifier 442 to render that controlled rectifier conductive. Current will then flow from terminal 342 via pump 540, terminal 362, resistor 440, and the anode-to-cathode circuit of that controlled rectifier; and that pump will respond to that flow of current to flex the flexible diaphragm thereof. and thereby force a quantity of air into the reservoir 534. Part of that air will pass through the vent 536 and be lost to the atmosphere, but other of that air will pass through the orifice 542 and enter the inflatable cuff 538', and the pressure transducer 544 will sense the pressure on the air within that inflatable cuff;

During the succeeding negative-going half-cycle of the AC applied to the terminal 342, the controlled rectifier 442 will be reverse-biased and will become nonconductive. During the next succeeding positive-going half-cycle of that AC, the current flowing through diode 345, resistors 344 and 346, and Zener diode 348 will again quickly develop the said predetermined voltage at the base-two of unijunction transistor 340; and the current flowing through the capacitor 354 will again quickly raise the voltage across that capacitor to theemitter peak-point voltage of that unijunction transistor. Consequently, that unijunction transistor will again become conductive, and the capacitor 354 will again discharge through the emitter-base-one circuit'of that unijunction transistor and through resistor 352 to again render the controlled rectifier 442 conductive. The resulting flow of current from terminal 342 via pump 540, terminal 362, resistor 440 and the anodeto-cathode circuit of that controlled rectifier will cause the flexible diaphragm of that pump to force further air into the reservoir 534.

The value of the current flowing through the resistors 368, 370, 382 and 396 and the diode 398 plus the value of the current flowing through resistor 404 and adjustable resistor 406 will be great enough to render the unijunction transistor 340, and hence the controlled rectifier 442, conductive during the early portion of each positive-going half-cycle of the AC applied to the terminal 342; and the pump 540 will respond to the resulting long on times of that controlled rectifier to force air into the reservoir 534 at a sufficiently rapid rate to cause the pressure in that reservoir, and hence in the inflatable cuff 538 and at the pressure transducer 544, to increase rapidly from atmospheric pressure to a value of 40 mm. of mercury. In the said one preferred embodiment of control system, the pressure in that inflatable cuff and at that pressure transducer will rise from atmospheric pressure to 40 mm. of mercury in about two seconds. The resulting rapid pressurization of the inflatable cuff 538 is desirable, because pressurization of that inflatable cuff at the normal pressurization rate would require an unduly long period of time. The value of 40 mm. of mercury was selected because it is lower than the diastolic blood pressure of most persons, but is high enough to enable a good part of the pressure needed within the inflatable cuff 538 to be developed rapidly. Another value of mercury could, of course, be selected, and could be incorporated into the operation of the pump controller 371.

As soon as the pressure transducer 544 senses a pressure in the inflatable cuff 538, and it will sense such a pressure almost as soon as the pump 540 starts pumping air into the reservoir 534. that pressure transducer will apply a negative-going signal to the terminal 484, and thus to the junction between tlie resistors 478 and 480 adjacent the transistor 486 of the operational amplifier 529. Those resistors and the resistors 476 and 482 constitute a voltage divider which establishes a positive voltage at the base of that transistor, and thereby renders that transistor conductive. The magnitude of the negative-going signal initially applied to the terminal 484, and hence to the base of the transistor 486, by the pressure transdiicer 544 will be small; but it will reduce the conductivity of that transistor. The operational amplifier 529 will respond to the reduction in conductivity of that transistor to apply a positive voltage to the terminals 394 and 395, and hence to the input terminal of the blood pressure meter 546 and to the cond'uctors 392 and 393. That blood pressure meter will respond to that positive voltage to cause the needle thereof to move upwardly to a position corresponding to the pressure in the inflatable cuff 538; and that meter will provide a readily readable indication of that pressure. The conductor 392 will apply that positive voltage to the resistor 388 and to the gate-tocathode circuit of controlled rectifier 386 via the shorting contacts 325 and 327 of switch 323 and the resistor 390; but that voltage will not be great enough to render that controlled rectifier conductive. The conductor 392 and the conductor 393 will apply that positive voltage to the resistor 420 and to the compensating network 429; and while a small amount of current might possibly flow via resistor 420, junctions 400 and 408, and capacitor 354 to ground and help charge that capacitor, substantially no current will flow through that compensating network because the Zener diode 427 will be nonconductive.

When the pressure within the inflatable cuff 538 increases to a value corresponding to 40 mm. of mercury, the negativegoing signal from the pressure transducer 544 will be great enough to cause the operational amplifier 529 to apply a positive voltage to the terminals 395 and 394 which will cause the needle of the blood pressure meter 546 to provide a reading of 40. That positive voltage also will be applied to the gate of controlled rectifier 386, and that voltage will be large enough to cause sufficient current to flow through the gate-to-cathode circuit of that controlled rectifier to render that controlled rectifier conductive. As that controlled rectifier becomes conductive, the voltage at the anode thereof, and hence at the anode of diode 398, will become less positive than the voltage at the cathode of that diode; and, thereupon, that diode will become back-biased. Thereafter, current will be unable to flow from terminal 161 via conductors 165 and 364, resistors 368, 370, 382, 396 and diode 398 to the capacitor 354 to charge that capacitor. Instead, the current flowing through the series-connected resistors 368, 370 and 382 will be bypassed to ground through the controlled rectifier 386; and the consequent reduction in charging rate of the capacitor 354 will cause the unijunction transistor 340, and hence the controlled rectifier 442, to become conductive later in the positive-going half-cycles of the AC applied to the terminal 342. The resulting shorter on times of that controlled rectifier will reduce the lengths of the strokes of the air pump 540, and will thereby decrease the rate at which the pressure in the reservoir 534. and hence in the inflatable cuff 538, will increase. However, the value of the current flowing from terminal 161 via conductors 165 and 364, resistor 404, adjustable resistor 406, junction 408, and capacitor 354 to ground will be great enough to provide on times for the unijunction transistor 340. and thus the controlled rectifier 442, which will enable air to be pumped into the reservoir 534 at a rate higher than the rate at which air can escape from that reservoir through the vent 536. As a result, the pressure within the inflatable cuff 538, and hence at the pressure transducer 544, will continue to rise, although at a slower rate. In the said one preferred embodiment of control system, that pressure will rise at the rate of 2 mm. of mercury per second.

The positive voltage which the operational amplifier 529 applies to the terminals 395 and 394 also will be applied to the resistor 420, and it will increase the value of the current which flows through that resistor to help charge the capacitor 354 However, that amount of current will be very small compared to the value of the current which flows through resistor 404 and adjustable resistor 406 to charge that capacitor As the pressure in the reservoir 534. and thus in the inflatable cuff 538, continues to increase. the pressure transducer 544 and the operational amplifier 529 will increase the positive voltage at the terminals 394 and 395. The blood pressure meter 546 will respond to that higher voltage to indicate that higher pressure; and the resistor 420 will respond to that higher voltage to supply a little more charging current to the capacitor 354. When the pressure in the reservoir 534. and thus in the inflatable cuff 538, reaches a level at which that inflatable cuff can occlude the artery in the person's finger suffciently to cause Korotkoff sounds to develop, the blood pressure circuit will render the transistor 336 conductive all as explained hereinafter in OPERATION OF BLOOD PRES- SURE ClRCUlT. At that time, the reading on the blood pressure meter 546 will indicate the persons diastolic blood pressure.

As the transistor 336 becomes conductive. it will effectively connect the capacitor 402 in parallel with the capacitor 354; and some of the current that formerly flowed through the capacitor 354 will thereafter flow through the capacitor 402. The reduced flow of current through the capacitor 354 will increase the length of time needed for the voltage across that capacitor to reach the emitter peak-point voltage of the unijunction transistor 340, and will thus cause the unijunction transistor and the controlled rectifier 442 to become conduc tive at a later time during each positive-going half-cycle of the AC applied to the terminal 342. The resulting shortened on" times of that controlled rectifier will reduce the lengths of the strokes of the pump 540; and, while that pump will continue to introduce air into the reservoir 534 during each stroke thereof, the rate at which that air is introduced into that reservoir will be less than the rate at which air can escape from that reservoir through the vent 536. Consequently, the pressure within the reservoir 534, and thus within the inflatable cuff 538, will decrease at a rate of 2 mm of mercury per second.

That decrease in pressure will quickly enable blood to flow once again through the artery in the persons finger; and that flow of blood is important, because it-will avoid numbness in that finger and will also prevent injury to that finger. The pressure transducer 544 and the operationalamplifier 529 will respond to that decrease in pressure to reduce the value of the positive voltage applied to the terminals 395 and 394; and the blood pressure meter 546 will respond to that lesser positive voltage to indicate the reduced pressure. The resistor 420 will respond to that lesser voltage to reduce the value of the current flowing therethrough to the capacitors 354 and 402.

As the blood again flows through the artery in the person's finger, the Korotkoff sounds will disappear; and W2 seconds after the last Korotkoff sound is sensed by the microphone 158, the transistor 336 will be rendered nonconductivc all as explained hereinafter in OPERATION OF BLOOD PRES- SURE ClRCUlT. As that transistor again becomes nonconductive. it will again isolate the capacitor 402 from the capacitor 354. The current which was flowing through the former capacitor will then add to the current flowing through the latter capacitor; and, once again, the unijunction transistor 340 and the controlled rectifier 442 will become conductive earlier in the positive-going half-cycles of the AC applied to the terminal 342. The increased on" times of that controlled rectifier will cause the pump 540 to supply air to the reservoir 534 at a rate which will enable the pressure in that reservoir, and hence in the inflatable cuff 538, to increase at the normal pressurization rate.

During the dcpressurization of the inflatable cuff 538, the pressure in that inflatable cuff decreased by a value equal to just a few millimeters of mercury; and hence the needle of the blood pressure meter 546 moved downwardly just a short distance. During the subsequent repressurization of that inflatable cuff, which will begin when the transistor 336 is again rendered nonconductivc, the pressure within that inflatable cuff will quickly rise to the level at which that inflatable cuff will again occlude the artery in the person's finger and again cause Korotkoff sounds to develop. As those Korotkoff sounds develop, the blood pressure circuit will again render the transistor 336 conductive; and the capacitor 402 will again be connected in parallel with the capacitor 354 with a consequent reduction in the "on" times of the controlled rectifier 442.

The transistor 336 will be alternately rendered conductive and nonconductive by the blood pressure circuit, and will thus cause the pressure in the inflatable cuff 538 to rccurrently decrease at the normal dcpressurization rate and then increase at the normal pressurization rate. That pressure will fall and then rise through a value equal to just a few millimeters of mercury during each dcpressurization and repressurization cycle; and hence the needle of the blood pressure meter 546 will remain close to a value which will correspond to the person's diastolic blood pressure. The transistor 336 will be alternately rendered conductive and nonconductive by the blood pressure circuit until the timer 369 renders the transistor 432 conductive. and thus prevents further charging of either of the capacitors 354 and 402 as explained hereinafter in OPERA- TlON OF TIMER 369. When the capacitors 354 and 402 are forced to remain uncharged, the unijunction transistor 340 and the controlled rectifier 442 will become inactive, and the pump 540 will be unable to pump further air into the reservoir 534. Air will, thereupon, leak out of that reservoir through the vent 536 until the pressure in that reservoir essentially reaches atmospheric pressure; and, at that time, the inflatable cuff 538 will apply essentially no pressure to the person's finger. The pressure in the reservoir 534 and in the inflatable cuff 538 will fall quite rapidly, because no air is being introduced into that reservoir by the pump 540. The pressure transducer 544 will respond to the decreasing pressure in the inflatable cuff 538 to rapidly reduce the value of the negative voltage which it applies to the input of the operational amplifier 529; and that operational amplifier will rapidly reduce the value of the positive voltage which it applies to the terminals 394 and 395'. That falling positive voltage will be applied to the input of the blood pressure meter 546.

The transistor 366 will be rendered conductive by the timer 369; and, thereupon, the voltage at the anode of the controlled rectifier 386 will fall close to ground potential. At such time, the value of the current flowing through that controlled rectifier will be too small to keep that controlled rectifier conductive; and that controlled rectifier will become nonconductive. This is important; because it means that at the start of the rendered conductive to keep the current flowing through resistors 368, 370 and 382 from reaching the capacitor 354 and the pressurization rate will decrease to the normal pressurization rate.

In the preceding portion of the description of the operation of the pump controller 371, it was assumed that the persons diastolic blood pressure was in the range of 40 200 mm. of mercury. During such a range of blood pressure. the pump controller 371 can provide a generally linear relationship between the on" time of the controlled rectifier 442 and the pressurization rate of the inflatable cuff 538. However, as the pressure in that inflatable cuff increases during that range, a given on time of that controlled rectifier will produce a lesser increase in pressure; because air tends to escape more rapidly through the vent 536 at higher pressures than at lower pressures, and because the pump 540 is somewhat less efficient at higher pressures than at lower pressures. Nevertheless, the inherent efficiency of the pump 540 is high enough. and the positive feedback of current to capacitor 354 through the resistor 420 is great enough, to make the relationship between the "on" time of the controlled rectifier 442 and the pressurization rate of the inflatable cuff 538 generally linear up to about 200 mm. of mercury.

At pressures above 200 mm. of mercury, the rate at which air escapes through the vent 536 increases so rapidly, and the efficiency of the pump 540 decreases so rapidly, that a given on" time of the controlled rectifier 442 would produce a materially smaller increase in pressure than the same *on time of that controlled rectifier could produce at pressures well below 200 mm. of mercury. it would be desirable to increase the on times of the controlled rectifier 442. beyond the durations of on" times called for by the signal from the pressure transducer 544, whenever the pressure in the inflatable cuff 538 is greater than 200 mm. of mercury; because such an increase in on" times would compensate for the increased rate at which air escapes through the vent 536 and for the decreased efficiency of the pump 540. The compensating network 429 provides such increases in the *on" times of the controlled rectifier 442 and it does so by causing the Zener diode 427 thereof to become conductive when the pressure in the inflatable cuff 538 is greater than 200 mm. of mercury.

The compensating network 429 always receives the positive signal which the pressure transducer 544 causes the operational amplifier 529 to apply to the terminals 394 and 395; but the Zener diode 427 of that compensation network is normally nonconductive. As a result, that Zener diode will normally keep current from flowing from terminal 394 via conductors 392 and 393, adjustable resistor 421, diode 425 and Zener diode 427, junctions 400 and 408, and capacitor 354" to ground. This means that throughout the range of pressures from -200 mm. of mercury, the compensating network 429 will be inactive. However, after the pressure in the inflatable cuff 538 increases above 200 mm. of mercury, the positivevoltage applied to the terminal 394 by the operational amplifier 529 will be great enough to render the Zener diode 427 of the compensating network 429 conductive. As that Zener diode becomes conductive. current will flow from terminal 394 via conductors 392 and 392, adjustable resistor 421, diode 425 and Zener diode 427, junctions 400 and 408, and

capacitor 354 to ground. That flow of current will be in addi-.

tion to the flow of current from terminal 161 via conductors 165 and 364, resistor 404, adjustable resistor 406, junction 408, and capacitor 354 to ground; and the total flow of current through that capacitor will increase the rate of charging of that capacitor. The resulting increase in on" time of the controlled rectifier 442, during each positive-going half-cycle of the AC applied to the terminal 342, will increase the length of each stroke of the pump 540 thereby enabling that pump to force sufficient air into the reservoir 534 to effectively cause the pressure in the inflatable cuff 538 to continue to increase at a rate close to the normal pressurization rate.

Because the diastolic blood pressures of most persons are below 200 mm. of mercury, the compensation network 429 is used only infrequently. However, for those persons whose diastolic blood pressures are above 200 mm. of mercury, that compensating network enables the control system of the present invention to monitor their diastolic blood pressures. Furthermore, that compensating network enables that control system to provide pressurization rates during the sensing of the diastolic blood pressures of those persons which are similar to the pressurization rates used during the sensing of the blood pressures of persons having more normal diastolic blood pressures thereby avoiding needless concern on the part of those persons or on the part of the operator of that control system.

Whenever the pressure in the inflatable cuff 538 falls below 200 mm. of mercury, the positive voltage applied to the terminals 394 and 395 by the operational amplifier 529 will decrease sufficiently to enable the Zener diode 427 to again become nonconductive. Thereupon, the positive feedback which the compensating network 429 was providing for the capacitor 354 will be cut off. That Zener diode will remain nonconductive, and will thus keep that compensating network from providing further positive feedback for that capacitor, until the pressure in the inflatable cuff 538 again exceeds 200 mm. of mercury.

If, somehow, the occlusion of the artery in the person's finger does not cause Korotkoff sounds to develop, or if, somehow, development of such sounds does not cause the blood pressure circuit to render the transistor 336 conductive, the controlled rectifier 442 will cause the pump 540 to con tinue to introduce air into the reservoir 534. The pressure in the reservoir 534 and in the inflatable cuff 538 will increase, in response to the continued introduction of air into that reservoir and as that pressure reaches a preset value --above 200 mm. of mercury but well below a value at which the finger of the person could be injured the pressure transducer 544 will cause the operational amplifier 529 to apply a positive voltage to the terminals 395 and 394 which will cause sufficient current to flow through resistor 422, the emitter-base circuit of transistor 424, diodes 436 and 438, conductor 439. junction 17!, and Zener diode 167 to ground to render that transistor conductive. That transistor and the transistor 432 are component parts of the pressure-limiting subcircuit 431. The resulting positive-going signal at the collector of transistor 424 will be applied to the base of transistor 432 and will render the latter transistor conductive thereby causing the voltages at the junctions 400 and 408 to drop to ground potential. As a result, the capacitor 354 will be unable to charge, and the unijunction transistor 340 and the controlled rectifier 442 will remain nonconductive. The resulting inactivity of the pump 540 will keep further air from being introduced into the reservoir 534, and the air in the inflatable cuff 538 and in that reservoir will escape to the atmosphere through the vent 536. As a result, the pressure within that inflatable cuff and within that reservoir will fall rapidly. Consequently, the person will be protected against injury, even if, somehow, Korotkoff sounds do not develop or the development of such sounds does not cause the blood pressure circuit to render the transistor 336 conductive.

Where the transistors 424 and 432 have been rendered con ductive by the development of the said preset pressure in the reservoir 534 and in the inflatable cuff 538, those transistors ,will remain conductive until the pressure in the inflatable cuff preset level to 30 mm. of mercury, those transistors will keep the pump 540 inactive. As the pressure in the inflatable cuff 538 falls to 30 mm. of mercury. the voltage applied to the terminal 394 by the operational amplifier 529 will not be great enough to cause sufficient current to flow through the emitterbase circuit of the transistor 424 to keep that transistor conductive; and hence that transistor will become nonconductive. As it does so, the transistor 432 also will become nonconductive; and this means that the voltage at the junctions 400 and 408 will be able to become positive with consequent charging of the capacitor 354.

It should thus be apparent that the pump controller 371 controls the on" times of the controlled rectifier 442, and thus controls the rate at which the pump 540 introduces air into the reservoir 534. That pump controller will coact with the fast pressurization circuit 399 to provide rapid pressurization of the inflatable cuff 538, until the pressure in that cuff equals 40 mm. of mercury. Thereafter, that pressure controller will provide reduced on times for the controlled rectifier 442, but will make those on times long enough to enable the pump 540 to provide normal pressurization of the inflatable cuff 538. After a Korotkoff sound is sensed by the microphone 158. the transistor 336- of the pressure controller 371 will be rendered conductive; and the on times of the controlled rectifier 442 will be further shortened. While the pump 540 will continue to supply air to the reservoir 534, air will escape through the vent 536 at a rate higher than the rate at which that pump supplies air to that reservoir. As a result, slow depressurization of the inflatable cuff 538 will occur. 1 /2 seconds after the last Korotkoff sounds are heard, the transistor 336 will be rendered nonconductive once again. and the inflatable cuff 538 will again be pressurized at the normal pressurization rate.

if the value of the pressure in the inflatable cuff 538 rises above 200 mm. of mercury, the pressure controller 371 will coact with the compensating network 429 to provide positive feedback for the capacitor 354 which will enable the pump 540 to continue to pressurize that inflatable cuff -and at a rate close to the normal pressurization rate. lf the value of the pressure in the inflatable cuff 538 rises to a preset value above 200 mm. of mercury, the pressure controller 371 will'coact with the pressure-limiting subeircuit 43l to halt further operation of the pump 540, until the pressure in the inflatable cuff 538 falls to 30 mm. of mercury.

The pump controller 371 is small and compact. it is inexpensive, it is substantially maintenance-free in operation, and it provides precise control of the pump 540. Furthermore, that pump controller obviates all need of solenoid-operated valves, relays, and other expensive components which require maintenance.

OPERATION OF HEART RATE CIRCUIT The electrodes which are affixed to the body of the person will sense a signal which will have the form of a characteristic electrocardiograph waveform. That signal will usually be in the range of l -5 millivolts; and the series-connected diodes 36 and 38 and the series-connected diodes 44 and 46 will remain nonconductive when such small voltage signals are developed across the terminals 30 and 32. As a result, the series-connected diodes 36 and 38 and the series-connected diodes 44 and 46 will not affect the signals which correspond to the electrocardiograph waveforms of the person.

The series-connected diodes 36 and 38, the series-connected diodes 44 and 46, the resistors 34 and 42, and the adjustable resistor 40 are important in the event a countershock must be applied to the body of a person whose heart is experiencing fibrillation. Countershocks having peak values of 1000 volts are sometimes applied to persons whose hearts are experiencing fibrillation; and a voltage of that magnitude could, absent the series-connected diodes 44 and 46, the series-connected diodes 36 and 38, the resistors 34 and 42 and the adjustable resistor 40, adversely affect the differential input amplifier within the block 58. By providing the seriesconnected diodes 36 and 38, the series-connected diodes 44 and 46, the resistors 34 and 42, and the adjustable resistor 40, the voltage which a countershock having a peak value of I000 volts could apply to the input of that differential input amplifier is limited to about seven-tenths of a volt. Consequently, the series-connected diodes 36 and 38, the series-connected diodes 44 and 46, the resistors 34 and 42, and the adjustable resistor 40 fully protect the differential input amplifier in the block 58 from injury.

The differential input amplifier in the block 58 will enhance signals having frequencies within the range of 20 90 c.p.s. and it will tend to attenuate signals-having frequencies appreciably above and appreciably below that range. As a result, the output of that amplifier will have a reduced content of transients, noise, and signals, from the electrodes connected to the terminals 30 and 32, which have frequencies appreciably above and below the range of 20 90 c.p.s. That differential input amplifier will respond to the signals which correspond to the persons electrocardiograph waveform; and an amplified analog-type signal corresponding to that electrocardiograph waveform will be applied to the terminal 74, and also will be applied to the base of the transistor 78 and to the anode of the diode 82. The positive-going components of that signal will forward-bias the diode 82. and will develop a voltage drop across the resistor 85 which will be coupled to the base of the transistor 86 by junctions 77 and 83, capacitor 84, and junction 73. Those positive-going components of that signal will render the transistor 78 more conductive, and thus will provide a negative-going signal at the left-hand terminal of the capacitor 79; and that capacitor will couple that negativegoing signal to the anode of the diode 80 thereby reverse-biasing that diode. The succeeding negative-going components of the signal from the transistor 72 will back-bias the diode 82: and they will render the transistor 78 less conductive. The resulting positive-going signal at the collector of that transistor will be coupled by the capacitor 79 to the diode 80; and that signal will forward-bias that diode and cause a voltage drop to develop across the resistor 85 which will be coupled to the base of the transistor 86 by junctions 77 and 83, capacitor 84. and junction 73. It will thus be noted that the transistor 78, the diodes 80 and 82, the capacitor 79, and the resistors associated with that transistor and those diodes coact with the capacitor 84 to couple the positive-going components of the signals from transistor 72 to the base of transistor 86, and to invert the negative-going components of those signals and then apply those inverted components to the base of that transistor. The capacitor 84 will tend to remove some low frequency components such as noise from the signals which it couples to the base of the transistor 86. Also that capacitor will tend to attenuate the P waves and the "T" waves of the person's characteristic electrocardiograph waveform; and, in

doing so, it will tend to keep those P waves and T" wavesv from triggering the rate network of the heart rate circuit.

The transistor 86 is connected as an emitter follower; and the capacitor 88 couples the signals at the emitter of that transistor to the base of transistor 90. The latter transistor is connected as'a stage of amplification, and it will amplify and invert the signals which appear at the emitter of the transistor 86. The diode 92 will bypass to ground the positive-going components of the signals which appear at the collector of the transistor and, as a result, the capacitor 93 will couple only negative-going components to the base of the transistor 94. The latter transistor also is connected as a stage of amplification arid it will amplify and'invert the negative-going signals coupled to the base thereof by the capacitor 93. The transistor 95 is connected as an emitter follower; and hence it will respond to positive-going signals applied to the base thereof to apply positive-going signals to the capacitor 96.

That capacitor, resistor 98, and conductor 101 will couple those positive-going signals to the input of phase-shift oscillator 99 in FIG. 2C, which is connected as a filter. That oscillator has the components thereof dimensioned to enable it to be shock-excited only by signals having frequencies close to 25 c.p.s. The output of that phase-shift oscillator is coupled by capacitor 111 and resistor 113 to the input of phase-shift oscillator 115, which also is connected as a filter. The components of the latter phase-shift oscillator also are dimensioned to enable that oscillator to be shock-excited only by signals having frequencies close to 25 c.p.s. The cascaded phase- shift oscillators 99 and 115 are particularly effective in rejecting signals and noise having frequencies appreciably below and appreciably above 25 c.p.s. This is important; because the electrodes affixed to the body ofa person can have signals applied to them which have frequencies that are fairly close to the desired frequency of 25 For example, the inflatable cuff 538 will apply an occluding force to the artery in the person's finger at a frequency of 60 c.p.s., and the electrodes to which the terminals 30 and 32 are connected can sometimes sense a signal of that frequency. Also, the pulse of a person can develop signals having frequencies below c.p.s. Further. muscular movements and changes in the position ofa person's body can cause signals of composite frequencies to be applied to those electrodes; and some of those frequencies can be fairly close to the desired frequency of 25 c.p.s. it would be undesirable to permit any of those signals to pass to the rate circuit 105 of the heart rate circuit, and the cascaded phaseshift oscillators 99 and 115 substantially completely reject such signals. As a result, the output from the phase-shift oscillator 115 is essentially a 25 c.p.s. signal; and that signal initially goes positive but, as that oscillator becomes shockexcited, goes heavily negative.

The negative-going signal from the output of the phase-shift oscillator 115 is coupled to the base of the transistor 119 by the capacitor 117; and that transistor is connected as a stage of amplification. That transistor will amplify and invert the signals applied to the base thereof thereby making those signals positive-going. The collector of the transistor 119 is connected to the base of the transistor 121; and the latter transistor is connected as an emitter follower. The level detector 120 will sense the level of the positive-going signals appearing at the emitter of the transistor 121, and it will apply to the capacitor 129 only those portions of those signals which exceed a predetermined level. That capacitor will couple those portions of those signals to the base of the transistor 131; and that transistor is connected as a high gain amplification stage. That transistor also will invert the signals applied to the base thereof, and will thus make those signals negative-going. The diode 135 will bypass to ground any positive-going components of the amplifier signals at the collector of the transistor 131; and the capacitor 141 will couple the negativegoing amplified signals to the input of the monostable multivibrator 145.

The components of the level detector 120 will preferably be dimensioned so only one particular wave of each electrocardiograph waveform will have sufficient amplitude to exceed the threshold value of that level detector. Because the R" wave of an electrocardiograph waveform will usually have an amplitude greater than the amplitude of any other wave of that waveform, the components of the level detector 120 will usually be dimensioned so only the upper portion of the R" wave of a persons characteristic electrocardiograph waveform will exceed the threshold value of that level detec- The right-hand transistor of the monostable multivibrator 145 will normally be conductive, and the left-hand transistor of that monostable multivibrator will normally be nonconductive. Each negative-going signal which corresponds to the *R" wave of a characteristic electrocardiograph waveform and which is applied to the base of that right-hand transistor will render that transistor nonconductive, and will render that lefthand transistor conductive. The resulting decrease in current of that monostable multivibrator will again become conductive and the left-hand transistor of that monostable multivibrator will again become nonconductive.

The positive voltages which appear at the output of the monostable multivibrator 145, whenever R" waves are sensed by the level detector 120, will be coupled to the terminal by the capacitor 147 and the diode 149, will be applied by conductor 137 to the rate circuit which includes the resistor 104 and the capacitor 102, and will be coupled to the base of transistor 136 by conductor 137, capacitor 132. and resistor 138. The positive voltages applied to the rate circuit 105 will charge the capacitor 102 and will thereby develop a voltage across that capacitor. The positive-going pulses which are coupled to the base of the transistor 136 by the capacitor 132 and the resistor 138 will render that transistor conductive; and, whenever that transistoi is rendered conductive, it will discharge the capacitor 144. During the intervals between the positive-going pulses from the monostable multivibrator 145, current flowing from terminal 51 via conductor 50, resistor 142. and capacitor 144 to the conductor 53 will charge that capacitor. The time constant of the series-connected resistor 142 and capacitor 144 will be long enough to keep the voltage developed across that capacitor from rendering the transistor 134 conductive, unless that capacitor is permitted to charge uninterruptedly for at least 5 seconds. This means that if the transistor 136 receives at least one pulse from the monostable multivibrator 145 during every 5 seconds, that transistor will discharge the capacitor 144 at least once every 5 seconds and will thus keep that capacitor from charging sufficiently to render the transistor 134 conductive.

On the other hand, if the person's heart did not, for a period as short as 5 seconds. develop an electrocardiograph waveform including an R wave capable of actuating the level detector 120, the monostable multivibrator 145 would be unable to provide a pulse which could render the transistor 136 conductive. In that event. the capacitor 144 would not be discharged; and. instead, would be able to charge uninterruptedly for 5 seconds. The voltage across that capacitor would increase to the point where it would render the transistor 134 conductive; and, as that transistor became conductive, current would flow from the upper terminal of capacitor 102 via junction 103, diodes 148 and 150. and the collector-emitter circuit of transistor 134 to ground. The resulting discharging of the capacitor 102 would cause the needle of the heart rate meter 33 to fall to zero. As that needle so fell, it would intercept the light beam between the lamp and photocell of the adjustable lower limit of that meter, and hence would cause the lamp 39 of the lower limit alarm circuit to be illuminated. Also, it would cause an alarm circuit, notshown, which included an audible signal to be actuated; and hence the operator of the control system would immediately be alerted to the fact that the patient's heart did not, for a period of 5 seconds, develop a characteristic waveform with an R" wave that exceeded the threshold value of the level detector 120.

The voltage developed across the capacitor 102 of the rate I circuit 105 will be coupled to the base of the transistor of the operational amplifier enclosed within the block 106. That operational amplifier will respond to that voltage to develop a DC voltage level, and it will apply that voltage level to the input of the heart rate meter 33. The time constant of that rate circuit will be long enough to avoid wide swings of the needle of that meter even when the heart rate of the person is abnormally low.

In most instances, the heart rate of a person will be fairly 1 regular; and, once the needle of the heart rate meter 33 has flow through the collector resistor of that right-hand terminal moved to a position indicating that heart rate, the operator of the control system can move the upper and lower adjustable alarm limits of that meter close to that position. If, subsequently, the heart rate of the person increases to a value above the upper alarm limit, the needle of that meter will intercept the light beam between the lamp and photocell of that upper alarm limit and will cause the lamp 41 of the upper alarm limit to become illuminated. Also, it will cause an alarm circuit, not shown, which includes an audible signal to be actuated. Immediately, therefore, the operator of the control system provided by the present invention will be alerted to the fact that the heart rate of the person has increased above the preset upper limit.

If, on the other hand, the heart rate of the person decreases to a value below the lower alarm limit, the needle of that meter will intercept the light beam between the lamp and photocell of that lower alarm limit and will cause the lamp 39 of that lower limit alarm circuit to become illuminated. Also, it will cause the alarm circuit, not shown, which includes the audible alarm to be actuated. Immediately, therefore, the operator of the control system will be alerted to the fact that the heart rate of the person has decreased below the preset lower limit.

Because the rate circuit 105 has a relatively long time constant, the capacitor 102 could not respond to a cardiac arrest to discharge quickly. However, the transistors 134 and 136 and the capacitor 144 will promptly discharge the capacitor 102, and thus permit the needle of the meter 33 to actuate the lower limit alarm of that meter, in the event ofa cardiac arrest all as explained hereinbefore.

The resistor 124 and the potentiometer 126 constitute a voltage divider connected between the conductor 139 and ground, and the movable contact of that potentiometer can be adjusted to zero the operational amplifier 106. Specifically, that movable contact can be adjusted so the operational amplifier 106 will provide an output of zero volts whenever no signals are applied to the rate circuit 105. The resistor 128 and the adjustable resistor 130 provide the calibration for the out put of the operational amplifier 106. Specifically, the movable contact of the adjustable resistor 130 can be adjusted to set the output at the emitter of the transistor 114 so the number of heart beats indicated by the needle of the heart rate meter 33 will correspond directly to the number of "R waves per minute developed by the persons heart.

The diodes 148 and 150 are desirable, because they will keep the needle of the heart rate meter 33 from moving downwardly below the zero position thereof whenever the person's heart does not, for a period of seconds, develop a characteristic cardiograph waveform including an R" wave having an amplitude exceeding the threshold value of the level detector 120. Absent the series-connected diodes 148 and 150, the capacitor 102 of the rate circuit 105 could discharge until the voltage at the junction 103 was essentially zero; and, in such event, the needle of the heart rate meter 33 might move below the zero position thereof. With those diodes. however, the voltage at the junction 103 will tend to remain at least I volt above ground potential.

OPERATION OF RESPIRATION RATE CIRCUIT The terminals 552 and 554 are connected, respectively; to the terminals 30 and 32 of the heart rate circuit, and thus are connected to the electrodes affixed to the body of the person. A free-running multivibrator in the block 590 will develop a 50 kc. waveform, and conductor 49 and the capacitors'592 and 594 will apply that 50 kc. waveform to the bases of the transistors 574 and 576. These transistors will act as a constant current generator, and they will apply that 50 kc. waveform to the tuned circuit which includes the capacitor 566 and the primary winding 564 of the transformer 5627 The secondary winding 560 of that transformer will coact with the capacitors 556 and 558, the terminals 552 and 554, and the electrodes affixed to the body of the person to couple that 50 kc. waveform to that persons body. The transthoracic impedance of that person's body will change as that person breathes, and that change in transthoracic impedance will appear as a change in loading" on the secondary winding 560 of the transformer 562; and that transformer will reflect that change in loading" back through the primary winding 564, junction 568, and conductor 109 to the block 590. As pointed out in detail in the said Horn and Kuni patent application, most of the 50 kc. waveform in the signals applied to the block 590 will be bypassed to ground; and, as a result, that block will provide a substantially ripple-free signal which corresponds to the respiration rate of the person. That signal will be amplified and will have the frequency thereof quadrupled in the block 572 and will then be applied to the input of the respiration rate meter 37. That meter will be calibrated so it will respond to the quadrupled-frequency signal to provide a reading which is directly proportional to the actual respiration rate of the person.

The high frequency signal developed by the free-running multivibrator in the block 590 is important in preventing polarization of the electrolyte that is used to assure good electrical contact between the skin of the person and the electrodes affixed to that skin. That electrolyte will tend to enact with that skin and with the metal of those electrodes to constitute electric batteries, and to develop a DC voltage between each of those electrodes and the persons skin. Such voltages would not be desirable; and they are completely obviated by the depolarization action of the high frequency signal which is passed continuously through the electrolyte by the respiration rate circuit.

The respiration rate of a person normally is fairly constant, and the needle of the respiration rate meter 37 will provide a substantially steady indication of that rate even where that respiration rate is abnormally low. Consequently, the upper alarm limit and the lower alarm limit of that respiration rate meter can be set close to the normal respiration rate of the person. If the respiration rate of that person increases sufficiently to cause the needle of the respiration rate meter 37 to intercept the light beam between the lamp and photocell of the upper alarm limit of that meter, the alarm circuit which includes the lamp 45 will illuminate that lamp. Also, that needle can actuate an alarm circuit, now shown. which includes an audible alarm; and hence that meter can immediately alert the operator of the control system to the fact that the respiration rate of the person has increased above its normal level. Similarly, if the respiration rate of the person decreases sufficiently to cause the needle of the respiration rate meter 37 to intercept the light beam between the lamp and photocell of the lower alarm limit ofthat meter, the alarm circuit which includes the lamp 43 will illuminate that lamp; Also, that needle can actuate an alarm circuit, not shown. which includes an available alarm; and hence that meter can immediately alert the operator of the control system to the fact that the respiration rate of the person has decreased below its normal level.

OPERATION OF BLOOD PRESSURE CIRCUIT As pointed out hercinbefore, the pump controller 371 will cause the controlled rectifier 442 thereof to actuate the pump 540, and thereby cause that pump to introduce sufficient air into the reservoir 534 to pressurize the inflatable cuff 538. As the pressure in that inflatable cuff increases, it will reacli a level at which that inflatable cuff will occlude the artery in the finger of the person; and, thereupon, perceptibly audible Korotkoff sounds will develop. The microphone 158 will sense those perceptibly audible Korotkoff sounds; and capacitor 160 will couple those sounds to the gate of the field effect transistor 162. The source of that field effect transistor is directly connected to the base of the transistor 174 of the cascaded band-pass filter and amplifier 259; and that cascaded band-pass filter and amplifier will enhance all signals having frequencies in the range of 40 c.p.s. through c.p.s. but will sharply attenuate signals having frequencies appreciably below 40 c.p.s. and appreciably above 120 c.p.s. The pulse of the person will cause signals to develop in that' persons finger, and the microphone 158 will sense these signals; but these signals will have frequencies below 15 c.p.s., and hence those signals will be sharply attenuated by the cascaded band-pass filter and amplifier 259. Also, transients and noise which can be caused by muscular movements or by movements of the person's body can develop signals which will be sensed by the microphone 158; but where those signals have frequencies appreciably below 40 c.p.s. or appreciably above 120 c.p.s., those signals will be sharply attenuated by the cascaded band-pass filter and amplifier 259. The overall result is that the cascaded band-pass amplifier and filter 259 will develop at the output thereof a signal which corresponds to the perceptibly audible Korotkoff sounds sensed by the microphone 158, and which is largely devoid of signals having frequenciesappreciably below 40 c.p.s. or appreciably above 120 c.p.s.

The emitter of the transistor 256 is the output of the cascaded band-pass filter and amplifier 259, and that emitter is coupled to the junction 268 by the conductor 274 and the capacitor 272. The collector of the transistor 247 is the output of the monostable multivibrator 239. and that output is connected to that junction by the diode 270. The And gate 295 will normally isolate the junction 268 from the base of transistor 282; but whenever both the cascaded band-pass filter and amplifier 259 and the monostable multivibrator 239 are applying signals to that junction, that And gate will couple that junction to the base of transistor 282.

Specifically, adjustable resistor 264. resistor 266. junction 268, and resistor 276 constitute a voltage divider connected between the conductors 165 and 233; and that voltage divider will tend to establish a slightly negative voltage at the anodes of diodes 270 and 284. However, diode 270, the collectoremitter circuit of transistor 247, diode 249. and resistor 243 are connected in series with each other and in parallel with the' resistor 276; and variations in the conductivity of that collector-emitter circuit can vary the voltage applied to the anodes of the diodes 270 and 284. For example, whenever the transistor 247 is nonconductive. the voltage at the junction 268 will be slightly negative, and will only moderately backbias the diode 284; but whenever that transistor is conductive. that voltage will be heavily negative. and it will sharply backbias that diode. The transistor 247 will normally be conductive, and hence the diode 284 will normally be sharply backbiased.

When the monostable multivibrator denoted by numberal 145 in FIG. 2C develops a rectangular positive-going pulse of 100 milliseconds duration and applies that pulse to the terminal 100, that pulse will be applied to the terminal 263 and will then be coupled by the conductor 265 and the capacitor 260 to the input of the monostable multivibrator 217. The latter monostable multivibrator will promptly render the transistor 221 thereof conductive and the transistor 225 thereof nonconductive; and it will thus develop a positivegoing pulse at the collector of the latter transistor. That pulse will have a duration of 130 milliseconds. and it will be coupled to the base of transistor 247 by the capacitor 262. That pulse will not affect the conductivity of that transistor. because that transistor is normally conductive.

The transistor 225 of the monostable multivibrator 217 will remain nonconductive for the said I30 milliseconds. but will thereafter again become conductive. The resulting negativegoing pulse at the collector of that transistor will be coupled to the base of transistor 247 by the capacitor 262; and that negative-going pulse will render the latter transistor nonconductive and the monostable multivibrator 239 will keep that latter transistor nonconductive for 170 milliseconds. This means that the voltage at the junction 268 will be only slightly negative, and that the diode 284 will be only moderately backbiased, for a period of I70 milliseconds.

The l30-millisecond period established by the monostable multivibrator 217 was initiated at the instant the persons heart contracted to start blood surging through that persons arteries. During that l30-millisecond period, part of that blood was moving toward, but had not reached. that persons fingers; and not until after the beginning of the l70-millisecond period could that blood reach the persons finger wherein the artery was being occluded. Because the diode 284 was sharply back-biased during the said 130-millisecond period, no sounds that were sensed by the microphone 158 during that period could forward-bias that diode and this is desirable because those sounds would not be Korotltoff sounds. However, after the beginning of the 170-millisecond period, the diode 284 was only moderately back-biased; and the cascaded band-pass filter and amplifier 259 could respond to signals, developed by the microphone 158 in response to perceptibly audible Korotkoff sounds, to apply positive-going signals to the junction 268 which would forward-bias the diode 284.

At the end of the 170-millisecond period, the monostable multivibrator 239 will again render the transistor 247 conductive; and, thereupon, the diode 284 will again be sharply backbiased. Thereafter. until a further contraction of the person's heart causes the heart rate circuit to apply a positive-going signal to the input of the monostable multivibrator 217, and that monostable multivibrator has after a delay of 130 milliseconds again caused the monostable multivibrator 239 to render the transistor 247 nonconductive for l30 milliseconds, the diode 284 cannot again be forward-biased. The overall result is that the sounds sensed by the microphone 158 will be wholly unable to cause forward-biasing of the diode 284 except during the l-millisecond periods, between adjacent heart contractions of the person, wherein the microphone 158 should be able to sense perceptibly audible Kortkoff sounds.

When the microphone l58 senses perceptibly audible Korotkoff sounds during the l70-millisecond period when the transistor 247 is nonconductive. the signals at the output of the cascaded band-pass filter and amplifier 259 will be coupled to the junction 268 by the capacitor 272; and those signals will forward-bias the diode 284. Thereupon, the transistor 278 will become conductive; and the resulting flow of current from conductor 165 through resistors 286 and 288 and the collector-to-cmitter circuit of that transistor will provide a negative-going pulse at the base of transistor 282. The latter transistor will then become conductive and will apply a positive-going pulse to the base of transistor 280, thereby immediately rendering the latter transistor conductive.

As the transistors 280 and 282 become conductive. current will flow from conductor 165 via resistor 286, transistor 280, resistors 294 and 296. the base-emitter circuit of transistor 298, and resistor 316 to the conductor 233: and further current will flow from conductor 165 via transistor 282, resistor 292. the resistors 294 and 296. the base-emitter circuit of transistor 298. and resistor 316 to the conductor 233. The amount of current flowing through the base-emitter circuit of the transistor 298 will render that transistor conductive; and the resulting increase in current flowing through the resistor 302 will develop a negative-going pulse at the base of the transistor 312, thereby rendering that transistor nonconductive. As a result. a positive-going signal will develop at the collector of that transistor; and that signal will be applied by the fixed and movable contacts 320 and 322 of switch 323, the junction 324, and the resistor 338 to the base of transistor 336. That signal will render the latter transistor conductive, and will thus connect the capacitor 402 in parallel with the capacitor 354. As explained hereinbefore in OPERATION OF PUMP CONTROLLER, the connecting of capacitor 402 in parallel with the capacitor 354 will prolong the charging time of the latter capacitor, will cause the unijunction transistor 340 and the controlled rectifier 442 to become conductive later in the positive-going half-cycles of the AC applied to the terminal 342, and will reduce the on times of that con- 7 trolled rectifier. Thereupon, pressurization of the inflatable capacitor will discharge through those transistors. Specifically, whenever the transistors 280 and 282 are nonconductive, the capacitor 300 will respond to current flowing from terminal 161 via conductor 165, capacitor 300, resistor 296, the base-emitter circuit of transistor 298, resistor 316, and conductor 233 to the terminal 261 to start charging. The capacitance of that capacitor and the sum of the ohmic resistances of resistors 296 and 316 and of the base-emitter circuit of transistor 298 will coact to provide a time constant for that timer which will be long enough to enable enough current to flow through that capacitor and through the base-emitter circuit of the transistor 298, for 1% seconds, to keep that transistor conductive. At the end of that lVz seconds, the amount of current flowing through that capacitor and through the base-emitter circuit of transistor 298 will decrease. to the point where that transistor will become nonconductive. Thereupon, the transistor 312 will again become conductive, and will render the transistor 336 nonconductive once again. The capacitor 402 will, at such time, be effectively isolated from the capacitor 354; and the latter capacitor will charge, once again, at its normal rate. This means that the unijunction transistor 340 and the controlled rectifier 442 will become conductive earlier in.the positive-going half-cycles of the AC applied to the terminal 342, and will increase the on" times of that controlled rectifier. Thereupon, depressurization of the inflatable cuff 538 will end and repressurization of that inflatable cuff will begin.

If at any time during the charging of the capacitor 300 the transistors 280 and 282 become conductive, those transistors will discharge that capacitor; and will thus require the timer 319 to start its charging period of one l'r': seconds all over again. Because the transistors 280 and 282 will be rendered conductive whenever signals, corresponding to perceptibly audible Korotkoff sounds, are being applied to the junction 268 by the cascaded band-pass filter and amplifier 259 during the l70-millisecond period established by the monostable multivibrator 239 the capacitor 300 will be unable to start its l/z-second charging period until after the perceptibly audible Korotoff sounds have disappeared. However, l z seconds after the last perceptibly audible Korotkoff sounds have been sensed, the capacitor 300 will have charged sufficiently to reduce the base-emitter current through the transistor 298 to the point where that transistor again becomes nonconductive.

It will thus be apparent that the blood pressure circuit provided by the present invention utilizes signals corresponding to perceptibly audible Korotkoff sounds to terminate the pressurization of the inflatable cuff 538 and to start depressurization of that inflatable cuff, uses those signals to continue depressurization of that inflatable cuff until the last perceptibly audible Korotkoff sound is sensed, and then continues the depressurization of that inflatable cuff for He seconds. The use of signals, corresponding to perceptibly audible Korotkoff sounds, to halt pressurization of the inflatable cuff 538 is desirable; because it obviates all need of using a pressure greater than the pressure actually needed to occlude the artery in the persons finger. As a result, the minimum pressure which can be used is the pressure that is used. The use of a timer to iniate repressurization of the inflatable cuff 538 is desirable; because it enables the reverse bias on the diode 284 to be made large enough -to keep random signals and noise applied to the junction 268 from forward-biasing that diode during the l70-millsecond period established by the monostable multivibrator 239, and yet makes certain that the pressure within that inflatable cuff will drop below the level of the persons diastolic blood pressure. Absent the timer 319, the reverse bias on the diode 284 would have to be made quite small during the l70-millisecond period established by the monostable multivibrator 239 so that even the barely audible Korotkoff sounds could develop signals which would continue the depressurization of the inflatable cuff 538 until the pressure in that inflatable cuff was below the persons diastolic blood pressure and such a small bias could permit random signals and noise applied to the junction 268 to forward-bias that diode and unduly continue the depressurization of that inflatable cuff.

The l-l/2-second period provided by the timer 319 can be shortened or lengthened, as desired; but that period should always be slightly longer than the period of time between suecessive Korotkoff sounds. If that period was made shorter than the period of time between successive Kortokff sounds, the timer 319 might coact with the transistors 298,312 and 336 to start repressurization of the inflatable cuff 538 while perceptibly audible Korotkoff sounds were still being sensed and thus at a time when the pressure in that inflatable cuff was still at or above the diastolic blood pressure of the person.

The time required for blood to flow from the heart to the finger of a person will vary from person to person; but it will almost invariably be longer than milliseconds but shorter than 300 milliseconds. Consequently, the blanking period of l30 milliseconds will practically never blank out any perceptibly audible Korotkoff sounds; and the perceptibly audible Korotkoff sounds will almost invariably be developed during the l70-millisecond period when the diode 284 is only moderately back-biased.

If a persons diastolic blood pressure is below 40 mm. of mercury, the cascaded band-pass filter and amplifer 259 may coact with .the microphone 158 and the monostable multivibrators 217 and 239 to render the transistor 336 conductive even before the pressure in the inflatable cuff 538 reaches 40 mm. of mercury. However, the resulting paralleling of capacitors 354 and 402 will only retard. and will not halt, the pressurization of that inflatable cuff; because the series- connccted resistors 368, 370, 382 and 396 and diode 398, as well as the series-connected resistor 404 and adjustable resistor 406, will be supplying current to those capacitors. As soon as the pressure in the inflatable cuff 538 reaches 40 mm. of mercury, the controlled rectifier 386 will become conductive and will back-bias the diode 398; and the capacitors 354 and 402 will no longer receive current through the series-connected resistors 368. 370. 382 and 396 and diode 398 receiving current primarily through the series-connected resistor 404 and adjustable resistor 406. The resulting longer charging time of the capacitor 354 will reduce the on" times of unijunction transistor 340 and of controlled rectifier 442 to such an extent that air will exhaust from the reservoir 534 through the vent 536 at a greater rate than the pump 540 can introduce air into that reservoir. Thereupon. the pressure within the inflatable cuff 538 will decrease until W2 seconds after the last perccptibly audible Korotkoff sound is sensed by the microphone 158. Subsequently, the pump controller 371 and the blood pressure circuit will cause the pressure in that inflatable cuff, and hence at the pressure transducer 544, to rise to and then fall slightly below that persons diastolic blood pressure and the blood pressure meter 546 will indicate that blood pressure.

As pointed out hereinbefore, the cascaded band-pass filter and amplifier 259 is very desirable because it provides sharp rejection of signals having frequencies appreciably below 40 c.p.s. or appreciably above I20 c.p.s. That cascaded bandpass filter and amplifier also is very desirable because it obviates all need of a gain control adjustment.

The diastolic blood pressure of a person normally is fairly constant and the needle of blood pressure meter 546 will provide a close indication of that blood pressure during each prcssure-sensing cycle even where that blood pressure is abnormally high or low. Consequently, the upper alarm limit and the lower alarm limit of that blood pressure meter can be set close to the normal diastolic blood pressure of the person. If the diastolic blood pressure of that person increases sufficiently to cause the needle of blood pressure meter 546 to interrupt the beam of light between the lamp and photocell of the upper alarm limit of that meter, the alarm circuit which includes lamp 550 will illuminate that lamp. Also, that needle can actuate an alarm circuit, not shown, which includes an audible alarm; and hence that meter can immediately alert the operator of the control system to the fact that the diastolic blood pressure of the person has increased above its normal level.

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